The Big Bang Theory Canceled CBS Series Not Returning for Season 13

Amy and Sheldon's wedding provides Sheldon with the information he needs to make a breakthrough in his symmetrical string theory. Meanwhile, their friends pick up Sheldon and Amy's families from the airport, and Mark Hamill agrees to officiate at the ceremony.

When Sheldon learns that his mother won't attend his wedding unless he invites his brother, Georgie, he and Leonard travel to Texas to end a family feud. Also, the Wolowitz kids inadvertently infest Amy, Bernadette, Wolowitz and Koothrappali with pinkeye.

Sheldon goes to Vegas to win money for science. Also, Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.

Sheldon's comic book store experiences changes when writer Neil Gaiman puts Stuart's store on the map. Also, Koothrappali takes credit for Penny's astronomical discovery, and friendships are threatened.

A brilliant but reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere, and Leonard, Raj and Howard go along for the trip. Also, Penny and Bernadette improvise after Amy doesn't like the tame bachelorette party they planned for her.

When Leonard learns Sheldon is the president of the tenants association, he decides to run against him. Also, Bernadette encourages Wolowitz and Koothrappali to find the owner of a drone after they find it in the backyard.

Penny gets the opportunity to host Bill Gates at work when his company wants to partner with her pharmaceutical company. Also, Leonard, Koothrappali and Wolowitz do everything in their power to meet him, while Sheldon thinks he is the victim of an April Fools prank.

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Also, Bernadette and Wolowitz have a hard time deciding who should stay at home with the kids and who should go back to work.

When Bernadette won't go into labor, all her friends try different tactics to get things started. Also, Wolowitz confronts Bernadette after Amy accidentally reveals she's already chosen their son's name.

When Sheldon petitions Wil Wheaton to appear on the new Professor Proton show, Wil offers a role to Amy instead. Also, Penny gets angry when she thinks the female protagonist in Leonard's novel is based on her.

Koothrappali finds himself in the middle of domestic drama when he learns the woman he's dating, Nell, has a very upset husband, Oliver. Also, when Sheldon rents his old room back for a quiet place to work, he drives Leonard crazy by being a model tenant.

When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Also, Bert the geologist replaces Wolowitz in the band Footprints on the Moon, and Sheldon finds Penny a surprising source of scientific inspiration.

To discover who would be most qualified to be best man and maid of honor at their wedding, Sheldon and Amy subject their friends to a series of secret experiments. Also, Penny reveals her true feelings about Amy.

Sheldon and Wolowitz plan birthday celebrations for Amy and Halley, respectively. Also, Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Also, Koothrappali "breaks up" with Wolowitz after realizing his best friend is actually hurting his confidence.

Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment. Also, a seven-year-old video reveals a secret about Leonard and Penny's relationship.

Leonard and Wolowitz are furious after they learn Sheldon went to work with the military behind their backs. Also, while Bernadette is on bed rest, she asks Raj to do some digging when she suspects Ruchi is trying to steal her job.

Sheldon and Bert collaborate on a research project, despite Sheldon's embarrassment. Also, Penny and Bernadette coach Koothrappali on how to navigate his relationship with Ruchi.

Sheldon goes head-to-head with Wil Wheaton for the role of the new Professor Proton. Also, Penny steps in to take care of Halley when Bernadette and Wolowitz both wind up on bed rest.

Sheldon and Koothrappali confide in Bernadette when they can't handle Amy and Wolowitz working together. Also, Penny and Leonard learn new tactics for how to deal Sheldon from an unlikely source.

Howard and Sheldon bond when they drive to the desert to shoot off a model rocket. Also, when Leonard's mom, Beverly, finds a new best friend in Penny, it rubs Leonard the wrong way.

As Sheldon stresses about picking a wedding date, Amy tries to convince him he has a more laid-back side. Also, Koothrappali and Stuart compete to win the heart of Bernadette's new coworker, Ruchi.

Leonard angers the university – and the entire physics community – after he gives an embarrassing interview. Also, Amy and Bernadette bond over having to hide their success from Sheldon and Howard.

Amy gives Sheldon an answer to his proposal while Howard and Bernadette struggle with some unexpected news.

The gang is concerned when Sheldon's former admirer, Dr. Ramona Nowitzki, resurfaces while Amy is away at Princeton.

After Leonard, Sheldon and Wolowitz celebrate the completion of the top secret air force project, they are met with an unpleasant surprise. Also, Amy is offered a summer position as a visiting researcher.

Leonard isn't thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack.

Howard and Bernadette have a hard time leaving Halley in day care when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Wolowitz as well as Amy on the same day. Also, Bernadette is nearing the end of her maternity leave and must return to work.

Leonard, Penny and Raj adjust to their new living arrangement, and Sheldon takes an interest in Amy's work.

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon's old room.

With Koothrappali cut off from his father's fortune, he appoints Sheldon to help him get out of debt. Also, Penny considers joining Leonard at Comic-Con.

Sheldon and Amy have their first fight since moving in together, and Koothrappali is shocked at the realities of financial independence when he stops receiving support from his father.

Leonard and Wolowitz try to distract Sheldon when he slows the progress of their guidance system. Also, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley.

Sheldon beta tests an MIT invention after hearing it can help him read people's emotions. Also, Leonard can't hide his feelings when Penny announces her brother is coming to town and Raj invites his ex-girlfriends over to give him dating advice.

Leonard and Penny ask for Sheldon's and Amy's help on putting the romance back in their marriage. Howard and Raj go to extreme lengths to stop the floor in Halley's bedroom from making noise.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas.

Sheldon and Amy attempt to have an intimate moment together to celebrate Amy's birthday; Bernadette and Wolowitz welcome their newborn baby to the world.

Sheldon and Leonard must divide up their possessions and remove Penny's things from 4B.

When Bert, a Caltech geologist, wins the MacArthur Genius fellowship, Sheldon is overcome with jealousy. Also, Wolowitz finds an old remote control Stephen Hawking action figure he invented.

After a successful experiment combining their genes, Sheldon will stop at nothing to convince Amy they should procreate. Also, Koothrappali is embarrassed to tell the gang what the new woman he's dating does for a living.

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment and they host an "on location" episode of "Fun With Flags" in Penny's apartment. Also, Leonard lets Penny decorate Sheldon's old room after he learns that she has been secretly moving Leonard's collectibles into storage.

Penny is surprised to learn she has fans of her performance in "Serial Ape-ist" when she attends Van Nuys Comic Con with Leonard. Also, Amy hosts a Sheldon-style brunch at Penny's apartment, and Wolowitz makes an impulsive purchase when he starts stressing out about the baby on the way.

Leonard and Penny must separate a quarreling Sheldon and Amy when their cohabitation does not go as planned, and Sheldon threatens to break off their relationship when Amy refuses to adhere to the bathroom schedule. Also, Howard and Bernadette find unexpected guests at their house when they decide to stay home from a planned vacation.

When Amy's apartment floods, she proposes a "cohabitation experiment" with Sheldon. Also, Howard and Bernadette are upset when Koothrappali learns the gender of the baby before they do.

Tensions rise when the boys struggle to complete their government project on time and Sheldon tries an energy drink to stay awake. Also, Penny and Amy go to a "party" at Bert the geologist's house, and Kooothrappali learns Bernadette's true feelings about her pregnancy when they clean out the future baby room.

Colonel Williams, an Air Force representative from the Department of Material Command sits down to talk with Wolowitz.

After Sheldon's mother and Leonard's father share an evening together, everyone deals with an awkward morning the following day. Also, Penny's family arrives for the ceremony, including her anxiety-ridden mother, Susan, and her drug dealing brother, Randall.

Chaos ensues when Leonard's recently divorced parents, Alfred and Beverly, and Sheldon's devoutly religious mother, Mary, come to town. Also, Wolowitz and Koothrappali think the government is out to get them when they are contacted about their guidance system.

Sheldon hires Stuart to spend the day with Amy when he'd rather go to a movie screening. Also, Leonard's mother, Beverly, comes to town and Penny struggles to make a connection with her.

The gang goes to a wine bar and runs into Penny's old boyfriend, Zack. Also, Bernadette gets stuck spending the evening with Sheldon when she can't go wine tasting with the group, and things don't go as planned when Koothrappali introduces his new girlfriend, Claire.

Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.

Sheldon spills a secret of Leonard's when the two take a weekend cabin trip with Penny and Amy. Also, when Koothrappali goes overboard with pregnancy gifts, Wolowitz and Bernadette must draw the line.

Amy is shocked at a revelation from Sheldon after she buys him a new laptop. Also, Koothrappali sells out Leonard and Wolowitz after they lie to their wives in order to attend an early screening of a movie.

Leonard, Sheldon, and Wolowitz run into problems when they file for a patent for their infinite persistence gyroscope. Also, Penny, Amy and Bernadette give Koothrappali dating advice when Emily reaches out to him after their breakup.

After more than nine years together, the gang finally celebrates Sheldon's birthday, surprising him with a special guest.

When the gang finds out about Bernadette's pregnancy, they celebrate by singing karaoke. Also, Bernadette is concerned when Wolowitz freaks out over her pregnancy announcement, and Wolowitz is convinced he must make more money to provide for the baby.

Sheldon and Amy host a live Valentine's Day episode of Fun with Flags, Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub and Raj is torn between Emily and the cute girl he met at the Comic Bookstore.

Sheldon's thrilled when his Meemaw comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl at the comic book store who makes him question his relationship with Emily.

After having to deal with a sick Sheldon, Leonard, Penny and the gang try to treat themselves to a Sheldon-free weekend.

Penny gets more than she bargained for when Leonard agrees to meet with a psychiatrist on her behalf. Also, Sheldon and Koothrappali collaborate on an astronomical discovery, and Wolowitz and Bernadette can't believe what they are feeling after Stuart moves out.

As the guys prepare to go to the premiere of the new Star Wars movie, Sheldon plans a special event for Amy's birthday. Also, Leonard, Wolowitz, and Koothrappali must decide who will take their extra Star Wars movie ticket.

Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon".

Sheldon and Amy try hanging out as friends when they spend Thanksgiving together at the aquarium. Also, Wolowitz reluctantly agrees to volunteer at the soup kitchen with Bernadette, Raj and Emily, and Penny discovers that Leonard knows more about her than she thought.

When Leonard, Penny and Bernadette learn that Amy is going out on a dinner date, the trio set out to spy on her and the guy. Meanwhile, Sheldon recruits Raj and Howard to find a woman for him, since they were responsible for getting Amy and him together.

While being interviewed for a documentary about Spock from "Star Trek", Sheldon struggles to suppress his emotions about his recent break-up with Amy. Also, Wolowitz and Bernadette butt heads over remodeling his childhood home.

In the midst of a nation-wide helium shortage, Sheldon and Leonard take desperate measures to get the supplies they need. Also, Penny and Bernadette download a dating app on Amy's phone to try and find her a new man.

The guys take a fencing lesson from Barry Kripke and Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, when Stuart struggles to get female customers at the Comic Book Store, Penny, Amy and Bernadette come by to help him out.

Sheldon learns of an impending change in his living arrangements and decides to revert back to 2003, a simpler time before he met Leonard and Penny. Also, Howard and Raj form a band to play at the Comic Book Store.

The guys surprise Leonard with a belated bachelor-party weekend in Mexico, but their plans hit a bump in the road when they get a flat tire on the way. Meanwhile, the girls lean on Penny to tell her unsuspecting family that she and Leonard eloped.

Leonard confronts the woman he kissed on the North Sea in an attempt to set Penny's mind at ease. Also, Sheldon films a special episode of "Fun with Flags" after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.

After driving to Vegas to get married, Penny struggles with Leonard's confession that he kissed another girl. Also, Sheldon doesn't know how to act after Amy pushes pause on their relationship.

In the Season 8 finale, Leonard and Penny are pressured to set a wedding date by Sheldon, whose relationship with Amy has taken an interesting turn.

Personalities collide when Sheldon and Leonard's mothers finally meet. Meanwhile, Howard finally decides to "man up" and do his fair share of the housework - but not without a little help from his friends.

Wolowitz questions his engineering abilities when he and Sheldon can't get a toy drone to fly. Meanwhile, a cancelled flight nearly prevents Leonard from giving the commencement address at his former high school, and Raj pits his parents against each other when his father cuts him off financially.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Also, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

When Sheldon and Amy build a blanket fort, they come to major crossroads in their relationship. Also, Wolowitz meets the half-brother he never knew he had, and when Penny is invited to appear on Wil Wheaton's podcast, she and Leonard have a huge, on-air argument.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to meet an idol. Also, when Bernadette and Howard battle over the fate of his Dr. Who TARDIS, Raj and Amy offer to settle the dispute with a game of ping pong.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. Also, a blackout at Mrs. Wolowitz's home leads to a final family dinner in her honor.

Trouble arises when Amy learns Sheldon has applied for a one-way mission to colonize Mars. Also, a trip to the pet store ends in a fight for Sheldon and Amy, Leonard surprises Penny with a very "adult" purchase, and, Raj is caught snooping in Emily's apartment.

As a joke, Sheldon and Penny try an experiment designed to make participants fall in love. Also, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a "zombie." And, after returning from Mrs. Wolowitz' funeral, Bernadette and Howard run into trouble at the airport.

Wolowitz receives some shocking news as everyone prepares for the reopening of Stuart's comic book store. Penny teaches Sheldon how to "let it go," but can't follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.

After Leonard and Sheldon co-publish a physics paper, they must defend themselves against criticism from an online bully. Also, girls' night finds Penny, Amy and Bernadette confronting embarrassing moments from their past.

The gang tries to help Sheldon when he becomes stuck in a rut at work by increasing his anxiety level. Howard teases Raj with a new game called "Cinnamon or Emily?"

Wolowitz tries to distract Raj, who is anxiously awaiting data from a space probe he helped launch. Meanwhile, Sheldon and Leonard go dress shopping with Penny and Amy.

On Christmas Eve, Amy plans a traditional Victorian dinner, while Raj, Leonard and Howard scramble to remove a pigeon that flew into the clean room at the university. To prove a point to Amy, a Scrooge-like Sheldon buys her the worst possible gift.

Sheldon says a tearful goodbye to "Fun with Flags." Also, Leonard, Howard and Raj look for something significant in a dead professor's research, and Bernadette is shocked to learn her co-workers' true feelings from Penny.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj's parents' impending divorce causes Howard and Bernadette to work on their own marriage.

When the gang recreates a high school prom on the roof the of the guys' apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

The guys try to help Penny out of an awkward work dilemma. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel. Meanwhile, Leonard and Penny seek advice from Wolowitz and Bernadette after they fight about money.

Amy and Bernadette accuse Penny of being a "buzzkill" after she gets an email from work during their Vegas weekend. Meanwhile, the guys try to invent something cool, but only come up with new ways to procrastinate.

Raj's honesty about his past comes back to haunt him after his girlfriend, Emily, is cold to Penny. Also, the guys consider becoming part-owners in Stuart's comic book store.

Wolowitz is nervous after NASA asks him to throw out the first pitch at a Los Angeles Angels game. Meanwhile, Leonard and Penny try to prove Sheldon wrong after he says that he and Amy are a "superior couple".

Sheldon is ordered to teach a class, and the gang is surprised when Howard signs up to take it; and tensions between Penny and Bernadette afford Amy an opportunity to play one against the other.

Leonard and Amy take an unexpected road trip to Arizona to pick up Sheldon. Meanwhile, Penny interviews for a job at Bernadette's company, and Howard is weirded out by Stuart's relationship with Mrs. Wolowitz.

Sheldon is forced to confront an uncertain future and considers a major move. Meanwhile, Raj and Emily take it to the next level, and Mrs. Wolowitz's injury is a major headache for Howard and Bernadette.

Bad day causes Penny to reevaluate her life choices - including Leonard. Meanwhile, Howard and Bernadette struggle to care for Mrs. Wolowitz, and Raj gets relationship advice from Sheldon.

Professor Proton helps Sheldon cope with grief, while Leonard turns a relationship milestone into a competition with Penny. Meanwhile, Amy and Bernadette make a "Star Wars Day" gift for the guys.

When Sheldon tries to be spontaneous, it leads to unexpected friction between Penny, Amy and Bernadette. Meanwhile, Raj seeks Howard's help in preparing for a date with Emily.

Sheldon faces a personal crisis after deciding he's wasting his time with string theory. Meanwhile, a double date between Raj, Emily and the Wolowitzes ends in embarrassment for Howard.

While Raj is wracked with guilt when he tries to date two women at once, Penny wrestles with whether to take a role in a cheesy movie and Sheldon is torn trying to choose between two gaming systems.

When Sheldon visits his Mom in Houston, he is forced to confront a new reality. Meanwhile, Raj's 'Murder Mystery' party starts some fights within the gang.

After the insults fly, Bernadette tries to broker the peace between Wolowitz and Sheldon. Meanwhile, Penny is offered an embarrassing movie role and Raj asks Amy to write to a woman on his behalf.

Leonard buys a dining room table and it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.

Love is in the air when Sheldon and Amy join Howard and Bernadette for a trip to wine country. Meanwhile, Leonard and Penny must rush Raj's dog to the vet.

After the guys can't get Comic-Con tickets, Sheldon tries to hold his own convention and winds up spending a wild night with James Earl Jones. Meanwhile, the girls see if they can act like "grown-ups".

Sheldon tries to relax after he is forced to take a vacation. Meanwhile, Leonard struggles to be supportive of Penny after she quits her job, and Bernadette seeks Stuart's help in replacing one of Howard's comic books.

When Penny's big acting break on NCIS is a bust, Leonard struggles to help her, which results in Penny asking Leonard a bold relationship question. Meanwhile, Sheldon tries to learn how to be funny and Raj tries to work on his "game" before talking to girls.

While Sheldon is away in Texas, everyone gathers to decorate the apartment Christmas tree, and they each realize how much he has changed their lives.

Leonard and Amy help Sheldon cope with the shame he's feeling after his accidental contribution to science is disproved. Meanwhile, Raj must stay with Howard and Bernadette for a week.

Sheldon protests when the gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

Leonard tries to keep Sheldon from overreacting when a past mistake comes to light, but Sheldon punishes Leonard by making him walk a mile in his shoes. Meanwhile, Penny confronts Raj's ex-girlfriend, Lucy.

Sheldon feels slighted when Professor Proton seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, Bill Nye. Meanwhile, Raj gets jealous when Howard crashes "girls' night".

Sheldon's major scientific breakthrough makes him feel like a fraud. Meanwhile, Howard's romantic gesture to Bernadette causes Penny to step up her game with Leonard.

Sheldon must decide how much "Amy time" is too much after she takes a job at his university. Meanwhile, Howard finds himself sleeping on Raj's couch after a fight with Bernadette.

Sheldon seeks revenge after Amy ruins one of his favorite movies. Meanwhile, Leonard discovers a way to get Penny to do anything, and Raj and Stuart create online dating profiles.

When the entire gang competes in a scavenger hunt designed by Raj, it brings out the best - and worst - in everyone.

Leonard's friendship with Sheldon is put to the test when he returns from the North Sea. Meanwhile, Wolowitz's relationship with his mother causes an unusual threat to his masculinity.

With Leonard away, Sheldon and Penny spend quality time together sharing intimate secrets. Also, Wolowitz helps Raj get over his ex-girlfriend.

New success for Leonard makes Sheldon very jealous and throws Penny for a loop. Meanwhile, Koothrappali pushes Lucy too far in their relationship.

When the girls' trip to Vegas falls through, the guys invite them to play Dungeons & Dragons, causing Sheldon and Amy's relationship to take an unexpected turn. Meanwhile, Koothrappali and Lucy go on a very awkward date.

Sheldon and Leonard hire Professor Proton, the host of their favorite childhood TV show, to perform. Also, Howard and Bernadette run into trouble babysitting Raj's dog.

Sheldon feels lost after one of his favorite TV shows gets canceled too soon and Amy tries to help him get over his compulsive need for closure. Meanwhile, Raj discovers a secret about his new love interest, Lucy.

Leonard, Sheldon and Raj fight for tenure at the University, and the competition heats up when the girls get involved.

Howard struggles with whether or not he should open a letter from his father, and Leonard and Penny throw a "grown-up" cocktail party at the apartment.

Leonard, Sheldon and Wolowitz speak to junior high girls about careers in science. Meanwhile, Koothrappali plans a date with Lucy.

After a terrible date, Koothrappali vows to never leave his apartment. Meanwhile, Penny actually impresses Sheldon with her acting skills.

While the guys try to give their significant others the perfect Valentine's Day, Raj and Stuart throw a "lonely people" party at the comic book store.

When Sheldon and Leonard fight, it affects Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.

Sheldon is forced to work with Barry Kripke and faces a crisis of confidence. Meanwhile, Howard and Raj spend $1,000 on action figures of themselves.

While the guys take a road trip to a comic book convention dressed as "Star Trek: The Next Generation" characters, the girls stay home and try to interpret a comic book.

Sheldon gets accused of sexual harassment at the University and winds up getting Leonard, Raj and Wolowitz in trouble.

Sheldon revisits some Christmas memories during a game of Dungeons and Dragons, while Penny, Bernadette and Amy try to find a girl for Koothrappali when he joins the girls for ladies' night.

Sheldon tries to nurse a sick Amy back to health, while Wolowitz prepares for an upcoming fishing trip with his father-in-law.

When the University reassigns Sheldon's parking spot to Wolowitz, their fight affects the whole gang.

Howard and Raj try to get to the bottom of why Sheldon disappears every afternoon at 2:45. Meanwhile, Leonard and Penny deal with jealousy in their relationship.

Wolowitz struggles with moving out of his mother's house. Meanwhile, Sheldon is caught in the middle of an argument between Amy and Wil Wheaton.

Sheldon's relationship with Stephen Hawking is threatened over a game of "Words with Friends," and Penny secretly enrolls in a class at the local college.

The gang celebrates Halloween at Stuart's comic book store. Meanwhile, Leonard seduces Penny with science.

When Wolowitz returns from space, he doesn't get the hero's welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.

Amy feels threatened when Sheldon hires a young female assistant, and the pressure of being in space takes its toll on Wolowitz.

When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. Meanwhile, in space, the other astronauts pick on Howard.

With his friends on dates, Raj must face his loneliness. Also, Wolowitz is caught in an argument between Bernadette and his mom, even while he's in space.

When Howard and Bernadette decide they want to be married before his NASA launch, the gang rushes to put on a wedding.

NASA reschedules Howard's mission, putting his and Bernadette's wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the bedroom.

Bernadette reconsiders marrying Howard after learning about his sexual history.

When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.

Penny buys Leonard and Sheldon "Star Trek" collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. Meanwhile, Raj decides he has met the "Future Mrs. Koothrappali" after his parents set him up on a date.

Sheldon chooses to play video games with the guys rather than go with Amy to her aunt's birthday party.

Sheldon's life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space.

When an office at the University opens up, Sheldon must compete for it with his archenemy, Kripke. Meanwhile, a gift from Amy makes Penny uncomfortable.

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab. Meanwhile, Bernadette wants Howard to sign a pre-nup.

Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.

Leonard and Penny experiment with dating, while Raj develops a peculiar relationship with his phone's virtual assistant.

Everything might change when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two.

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and Howard must come to grips with Bernadette's dislike of children.

Leonard must face his fears after being contacted by his high school tormentor.

Sheldon considers taking his relationship with Amy to the next level when Stuart from the comic book store asks her out on a date.

Leonard and Penny try hanging out alone, and Sheldon must overcome his fear of birds.

Amy is crushed when Bernadette and Penny go shopping for wedding dresses without her.

Cute comic book artist puts Leonard and Priya's relationship to the test, while Sheldon tries to scare the guys for Halloween.

Sheldon competes with the gang for his mother's attention when she comes to visit.

Sheldon and Leonard get invited to a party at Wil Wheaton's house, and Howard gets an out-of-this-world opportunity.

Raj finally meets a girl he can communicate with.

Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.

Fight between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya.

Penny worries that she's screwed things up permanently with her friends, while Sheldon takes command of the paintball team.

When Bernadette receives her Ph.D., the guys take joy in reminding an emasculated Wolowitz that he is the only one in their group who isn't a doctor. Meanwhile, Koothrappali becomes Sheldon's new roommate after hearing Leonard and Priya engaging in a "Star Trek" bedroom fantasy.

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

When Priya uses her lawyer skills to pick apart the roommate agreement, the girls take Sheldon dancing.

Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette.

When someone hacks Sheldon's online game account, the guys go on a quest to find the culprit.

Leonard must choose between new girlfriend Priya and his friendship with Penny. Meanwhile, Howard drives Sheldon crazy with a magic trick.

Sheldon struggles to cope when he realizes it's actually Leonard who is the center of their social group.

As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.

Sheldon hopes acting lessons from Penny will help him become a better teacher. Meanwhile, Koothrappali fantasizes about his best friend's girlfriend.

Tension runs high when everyone is staying at the same hotel for a science event and Bernadette runs into her ex-boyfriend.

Leonard's idea for a smartphone app derails his friendship with Sheldon.

The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.

Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.

Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.

While the guys camp in line for a screening, Penny and Bernadette invite Amy to her first slumber party.

Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.

Leonard keeps an affair secret from Sheldon, Howard and Raj.

Leonard realizes he's the only one without a girlfriend, while Sheldon wants to get rid of his.

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.

The guys are concerned as Sheldon searches for an alternative to human companionship.

Sheldon realizes he won't live long enough to download his consciousness into a robot body, and attempts to extend his lifespan.

Penny finds herself along for the ride on Sheldon's first date ever; while Wolowitz finds a new use for a robotic arm.

While Penny worries that dating Leonard has ruined her for normal guys, Wolowitz and Koothrappali search for Sheldon's perfect match online.

Leonard tells Penny about how he met Sheldon for the first time...and what happened to the elevator.

Leonard and Sheldon compete for the attention of a famous female physicist.

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy.

Fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

When the guys find a ring from "The Lord of the Rings" at a garage sale, it threatens to tear them apart.

Sheldon winds up in traffic court when he gets a ticket because of Penny.

Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider in Switzerland on Valentine's Day.

Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

While Sheldon and Koothrappali attend a university mixer, Leonard is upset to discover that Penny believes in psychics.

Visit from Leonard's mother delights Sheldon and horrifies Leonard.

Sheldon attempts to help Penny understand Leonard's work, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

An argument between Leonard and Penny proves "inconvenient" to Sheldon.

Sheldon teaches Leonard how to understand football while a kite-fighting incident threatens Howard and Raj's friendship.

While Sheldon settles a score with his nemesis, Wil Wheaton, Wolowitz begs Leonard to get Penny to set him up with one of her friends.

Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as third wheel.

Howard and Raj visit a Goth nightclub to pick up women while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.

Sheldon flees back to Texas in disgrace when he learns the guys tampered with his arctic expedition data, forcing the guys to follow him and threatening Leonard's hopes for a romantic encounter with Penny.

Penny is conflicted when Leonard and his friends decide to spend the summer working - at the North Pole.

Things begin to look up for Leonard when Penny makes a surprising revelation on her second date with Stuart. Meanwhile, Wolowitz enlists his friends' help when he discovers a critical design flaw in his project for NASA.

Leonard and Koothrappali take a heartbroken Wolowitz to Las Vegas, leaving Sheldon locked out of his apartment and forced to bunk with Penny.

While a fellow comic book-loving pal of the guys romances Penny, Leonard and Wolowitz venture out into the world of "Ladies' Night" at a local bar.

Penny develops a rivalry with a sexy female neighbor who threatens to become "The New Penny" in the building.

Penny's home hair products business becomes a complete nightmare when a caffeine-addled Sheldon takes over.

Train trip to San Francisco takes a major detour when Leonard, Sheldon, Wolowitz and Raj discover that beautiful sci-fi actress Summer Glau is onboard.

Paintball game leads to a fight between Penny and Sheldon, and romance for Wolowitz and Leslie.

Disastrous visit from Mrs. Hofstadter brings Leonard and Penny closer together.

Sheldon's "simple" solution to Penny's financial problem leads to a confrontation between Leonard and Penny's hulking ex-boyfriend, Kurt.

Socially awkward Sheldon develops a scientific procedure for making friends.

When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important team-mate in an upcoming fighting robot competition.

Christmas is a source of stress for Leonard - whose handsome colleague starts dating Penny - and his friends, who are being tormented by Sheldon's obsession with gift-giving etiquette.

When Leonard's relationship with a new woman starts moving too fast, he goes to Penny for advice.

Sheldon can barely contain his joy when Leonard starts dating a woman who meets Sheldon's exacting standards.

Wolowitz thinks he's found the love of his life, until she meets Leonard.

Penny vows to get revenge on Sheldon when he bans her from the apartment for a series of petty infractions.

Young grad student's attraction to Sheldon confuses everyone, including Sheldon himself.

Leonard and his friends stage an intervention to make Sheldon confront his longstanding fear of driving.

Raj, newly famous because of an article in a magazine, gets a big head and makes a disastrous play for Leonard's crush, Penny.

Sheldon creates a monster when he introduces Penny to the world of online gaming.

When Leonard sees Penny with a handsome new guy, he enters into a rebound relationship with Sheldon's nemesis, Leslie Winkle.

After her first date with Leonard goes awry, Penny finds an unwilling confidant in Leonard's anti-social roommate, Sheldon.

When Leonard asks Penny out on a date and she says yes, they each seek the "wisdom" of reluctant advisor.

When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party, but is sidetracked by Sheldon who unexpectedly gets to live out one of his greatest fantasies at an electronics store.

When Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Leonard devises a plan to eliminate his rivals, however, it backfires when Sheldon declares he will decide whom his sister dates.

When Leonard and the guys buy a time machine prop from a classic 1960 movie, its arrival creates problems for Penny and she tells the boys that their obsession with comics and toys is "pathetic".

Since Sheldon's only focus is to prove his mental superiority while preparing for the Physics Bowl, the guys kick him off the team and enlist his nemesis Leslie Winkle.

When Leonard and Sheldon meet a 15-year-old physics prodigy, Sheldon is distraught that this boy genius is younger and smarter, so in an attempt to restore his sense of purpose, the boys come up with a solution to derail Dennis' research.

When Sheldon gets sick, Leonard and the boys know what's in store and avoid him like the plague, leaving an unsuspecting Penny to nurse the world's worst patient back to health.

After hearing Penny sing, Leonard lies to avoid seeing her perform, but Sheldon takes it one step further with a more elaborate lie that leads to the appearance of his non-existent cousin.

When Sheldon and Leonard are invited to present their joint findings at a physics conference, Sheldon refuses, and Penny steps in to mediate, only deepening the rift between the two best friends.

Koothrappali is overwhelmed after his parents arrange a blind date, but he discovers he actually can talk to the opposite sex after a few drinks; however, complications set in when his beautiful date is more interested in Sheldon.

When Wolowitz seduces Penny's friend and takes over her apartment, Penny sleeps on Leonard and Sheldon's couch. With Wolowitz preoccupied, the guys discover they are without a fourth member of their group and in desperation, they ask Penny to join their Halo team.

Leonard, Sheldon, Wolowitz and Koothrappali undertake a challenging and risky experiment-attending the Halloween party being thrown by their hot neighbor, Penny.

After sensing his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle.

When Sheldon gets fired, he explores life beyond physics, but his initial thrill of shopping with Penny devolves over time to him weaving ponchos as a shut-in, forcing Leonard to call on Sheldon's mother.

Leonard is bummed to learn that his crush, Penny, is seeing someone, so encouraged by his friends and fellow scientists, Leonard actually summons the nerve to ask a woman out on a date.

Leonard volunteers to sign for a package, hoping to make a good impression on Penny. When he enlists the help of his obsessive-compulsive roommate, Sheldon, his attempt at chivalry goes horribly awry.

Is a comedy about brilliant physicists, Leonard and Sheldon, who are the kind of "beautiful minds" that understand how the universe works. But none of that genius helps them interact with people, especially women. All this begins to change when a free-spirited beauty named Penny moves in next door. Sheldon, Leonard's roommate, is quite content spending his nights playing Klingon Boggle with their socially dysfunctional friends, fellow Cal Tech scientists Wolowitz and Koothrappali. However, Leonard sees in Penny a whole new universe of possibilities... including love.

Fans of much-loved sitcom The Big Bang Theory, including Sofie Hagen, Joe Swash and Jamie Laing, discuss the biggest, funniest and nerdiest moments from the show and reveal their favourite clips

During this 30-minute special retrospective, series stars Johnny Galecki and Kaley Cuoco take viewers behind the scenes of the longest-running multi-camera comedy series in television history.

In the special, Galecki and Cuoco will lead fans on a trip down memory lane, sharing some of the best-kept backstage secrets and personal memories from the past 12 years. They will reveal their favorite moments playing beloved characters Leonard and Penny, and revisit some of the most memorable stories from "The Big Bang Theory Stage." In addition, the special will feature a tour of the iconic sets, including Leonard and Sheldon's apartment.