Leonard Hofstadter and Sheldon Cooper are both brilliant physicists working at Cal Tech in Pasadena, California. They are colleagues, best friends, and roommates, although in all capacities their relationship is always tested primarily by Sheldon's regimented, deeply eccentric, and non-conventional ways. They are also friends with their Cal Tech colleagues mechanical engineer Howard Wolowitz and astrophysicist Rajesh Koothrappali. The foursome spend their time working on their individual work projects, playing video games, watching science-fiction movies, or reading comic books. As they are self-professed nerds, all have little or no luck with women. When Penny, a pretty woman and an aspiring actress from Omaha, moves into the apartment across the hall from Leonard and Sheldon's, Leonard has another aspiration in life, namely to get Penny to be his girlfriend.
Sheldon and Amy have their first fight since moving in together and ..
Leonard and Wolowitz try to distract Sheldon when he slows the progr..
Sheldon uses a machine to help him identify other people's emotions,..
Leonard and Penny may need a Relationship Agreement, and Sheldon vol..
Sheldon and Amy visit Leonard and Penny for the first time since the..
Amy's desire to have an intimate night with Sheldon on her birthday ..
Sheldon and Leonard must divide up their possessions and remove Penn..
When Bert, a Caltech geologist, wins the MacArthur Genius fellowship..
After a successful experiment combining their genes, Sheldon will st..
In order to continue living with Sheldon, Amy lies to him about repa..
Penny learns there are fans of her performance in ``Serial Ape-ist''..
Leonard and Penny must separate a quarreling Sheldon and Amy when th..
When Amy's apartment floods, she proposes a cohabitation experiment ..
Sheldon can't keep up with the late nights Howard and Leonard are pu..
The Air Force shows interest in the guidance system and Penny lets i..
After Sheldon’s mother and Leonard's father share an evening toget..
Leonard and Penny get remarried in front of their friends (who show ..
Sheldon hires Stuart to spend the day with Amy when he’d rather go..
The gang goes to a wine bar and runs into Penny’s old boyfriend, Z..
Everyone must choose sides when a small argument between Leonard and..
Secrets are revealed when Amy and Sheldon join Penny and Leonard on ..
Amy is shocked at a revelation from Sheldon after she buys him a new..
Leonard, Sheldon and Wolowitz file for a patent on their new inventi..
For the first time in nine years, the gang celebrates Sheldon's birt..
The gang celebrates news of Bernadette's pregnancy by singing karaok..
Amy and Sheldon host a Valentine's Day edition of Fun With Flags; Pe..
Sheldon's excitement about his Meemaw's visit fades when she butts h..
After dealing with Sheldon while he was sick, Leonard, Penny and the..
Leonard visits a psychiatrist so Penny can make a sales call. Stuart..
After dating for more than five years, Amy and Sheldon spend the nig..
Sheldon has a song stuck in his head; despite their awkward date, Am..
Amy and Sheldon spend Thanksgiving at the aquarium -- as friends; Wo..
When Leonard, Penny and Bernadette learn that Amy is going out on a ..
While being interviewed for a documentary about Spock from "Star Tre..
Leonard and Sheldon go to great lengths to secure the helium they ne..
Barry Kripke expresses interest in Amy while leading a fencing lesso..
Sheldon reverts back to 2003 when he learns that Leonard and Penny a..
A flat tire during Leonard's bachelor party weekend in Mexico tests ..
Leonard confronts the woman he kissed on the North Sea in an attempt..
Sheldon is confronted by a mystery of the universe he cannot unravel..
While facing relationship changes, Sheldon pushes Penny and Leonard ..
While facing relationship changes, Sheldon pushes Penny and Leonard ..
When Sheldon's and Leonard's mothers finally meet, personalities col..
Wolowitz questions his engineering skills; a canceled flight puts Le..
The guys fight over a message that could be used for alien contact.
Howard discovers a family secret. Sheldon and Amy build a fort. Penn..
A speaking engagement at UC Berkeley puts Leonard and Sheldon in a g..
When the loss of electricity in the Wolowitz house leads to the defr..
Amy and Sheldon buy a pet turtle together. Sheldon plans on becoming..
Penny agrees to be part of Sheldon's intimacy experiment. Meanwhile,..
Sheldon becomes annoyed after discovering that Amy has been helping ..
Sheldon and Leonard must defend themselves from an online bully's cr..
The gang tries to help Sheldon when he becomes stuck in a rut at wor..
Raj is concerned over whether a probe he designed will work in outer..
Christmas Eve, Amy plans a traditional Victorian dinner, while Raj, ..
Howard, Leonard and Raj look through their dead professor's research.
Leonard has minor surgery on his nose, causing Sheldon to overreact.
Sheldon feels pressured to participate in traditions when the gang r..
The guys try to help when Penny is faced with an awkward dilemma at ..
Raj and Sheldon try to simulate a dark-matter research expedition; P..
During their weekend in Las Vegas, Bernadette and Amy accuse Penny o..
Raj's honesty comes back to haunt him when his new girlfriend is unf..
Wolowitz feels nervous when he is asked to throw the first pitch at ..
Amy takes advantage of the tension between Penny and Bernadette.
Leonard and Amy take an unexpected road trip to Arizona to pick up S..
In the Season 7 finale, Sheldon gets caught up in all the life-alter..
A bad day compels Penny to re-evaluate her choices -- including Leon..
A grief-stricken Sheldon receives counseling from his childhood TV i..
Sheldon gives spontaneity a try; Raj asks Howard for help with prepa..
Raj and Emily double-date with the Wolowitzes, and Howard becomes fl..
Raj struggles with guilt when he dates two women at once; Penny has ..
Sheldon is faced with a new reality when he visits his mom in Housto..
Things turn rocky between Sheldon and Wolowitz after a barrage of in..
Penny ponders the potential purchase of a dining-room table for Leon..
Sheldon and Amy go on a trip to wine country with Howard and Bernade..
Unable to score tickets for Comic-Con, Sheldon decides to stage his ..
There's impactful news on the work front as Penny makes a big step t..
As Leonard tries to help Penny with a disappointment, Penny asks him..
While Sheldon is in Texas, the rest of the gang realize how much he ..
Amy and Leonard try to help Sheldon deal with his shame; Raj stays w..
Howard's mother has a say when he and Bernadette host Thanksgiving d..
Leonard fails to stop Sheldon from overreacting after a past slight ..
When Sheldon's childhood hero, Professor Proton, seeks Leonard's hel..
Sheldon makes a major scientific breakthrough, but he feels it may h..
Sheldon and Amy's relationship is tested when she takes a job at his..
Sheldon wants revenge after Amy ruins one of his favorite films; Leo..
Raj designs a scavenger hunt that brings out the best -- and the wor..
Leonard and Sheldon's friendship is tested; Wolowitz's relationship ..
Sheldon and Penny share secrets while Leonard is away; Wolowitz help..
When Leonard is offered an exciting opportunity to work overseas, Pe..
Amy and Sheldon's relationship takes a surprising turn during a game..
Leonard and Sheldon hire the host (Bob Newhart) of their favorite ch..
Amy tries to help Sheldon get over his compulsive need for closure w..
The guys' competition for a tenured professorship leads them to sham..
Howard considers whether or not he should open a letter from his fat..
Leonard, Sheldon and Wolowitz talk to junior high girls about scienc..
Koothrappali is put out when his date walks out in the middle of the..
Leonard arranges a magical Valentine's Day dinner date for Penny, bu..
Leonard and Sheldon get into a spat that sends Leonard across the ha..
Sheldon faces a crisis of confidence when he is forced to work with ..
While the guys take a road trip to a comic book convention dressed a..
When Sheldon is accused of sexual harassment, he ends up getting Raj..
During a game, Sheldon revisits Christmas memories; Amy, Penny and B..
Amy takes ill and Sheldon becomes her nursemaid, while Wolowitz take..
When the University reassigns Sheldon’s parking spot to Wolowitz, ..
Aired: November 15, 2012
Raj and Howard try to figure ou..
Wolowitz struggles with moving out of his mother’s house. Meanwhil..
A disagreement over a game of Words With Friends endangers Sheldon's..
The gang celebrates Halloween at Stuart?s comic book store. Meanwhil..
Wolowitz is disappointed when he doesn't receive a hero's welcome up..
Amy feels threatened when Sheldon hires a young female assistant. Me..
Sheldon uncovers a secret about Penny and Leonard; and in space, the..
Season 6 blasts off with Wolowitz in space, and despite that, he sti..
The fifth season ends with Howard and Bernadette deciding to get mar..
When NASA reschedules the launch of Howard's mission, the countdown ..
Bernadette has second thoughts about marrying Wolowitz when details ..
Sheldon is in seventh heaven and prepared to do whatever it takes to..
Raj may have found his soul mate after his parents set him up on a d..
Sheldon opts to spend a weekend playing video games with the guys in..
After his barber is hospitalized, Sheldon undergoes a hair-raising c..
Sheldon and Kripke square off in a series of sports-related competit..
Sheldon takes it easy by working with Amy at her neurobiology lab af..
The friendship contract is in danger of being nullified when Leonard..
Leonard and Penny give dating another try, while Raj begins a rather..
Everything might change when Leonard offers Penny a spur of the mome..
Amy is upset with Sheldon when he isn't impressed with her recent ac..
Leonard confronts his fears when he's contacted by a bully who torme..
Sheldon becomes jealous when Stuart from the comic-book store asks A..
Leonard and Penny attempt to hang out alone; and Sheldon tries to ov..
Amy is crushed when Bernadette and Penny go shopping for wedding dre..
Leonard feels threatened when a charming comic-book artist comes bet..
Sheldon's mom visits, and he competes for her attention, which seems..
Leonard and Sheldon attend a party at the home of Sheldon's nemesis,..
Raj meets a woman with whom he's able to talk.
Leonard and Amy get to know each other better, while Howard and Bern..
Penny and Sheldon clash, and Amy is caught in the middle of their ba..
In the fifth-season opener, Penny hits a low point when she realizes..
The Big Bang Theory It All Started With A Big Bang
a 25 min s..
In the fourth-season finale, Raj moves in with Sheldon when Leonard ..
Howard finally tells his mother that he's marrying Bernadette, and t..
Raj makes an attempt to cure his phobia of talking to women; and Pen..
Priya uses her legal expertise to rip apart Sheldon's roommate agree..
Sheldon and Amy spread gossip as part of an experiment; and Howard a..
The guys become sleuths to find out who hacked Sheldon's online-game..
Leonard is forced to choose between Penny and his new girlfriend, Pr..
Sheldon is upset when he realizes Leonard is the center of their gro..
Wolowitz considers taking things with Bernadette to the next level; ..
A wealthy donor makes Leonard question what he is willing to do for ..
Sheldon takes acting lessons from Penny in hope of becoming a better..
Bernadette runs into her ex-boyfriend (Rick Fox) while attending a s..
Leonard's idea for a smartphone app derails his friendship with Shel..
The guys enter a costume contest with Penny's new boyfriend.
Amy realizes she has feelings for Penny's ex; Koothrappali and Wolow..
Penny asks Leonard to lie to her father (Keith Carradine); Howard, R..
While the guys camp out for a long-awaited movie screening, Penny an..
Howard baffles Sheldon when he won't accept his apology; and an FBI ..
Leonard keeps an affair secret from Sheldon, Howard and Raj.
Leonard realizes he's the only one without a girlfriend, while Sheld..
An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon ge..
When Sheldon searches for an alternative to human companionship, the..
Realizing he will not live long enough to download his consciousness..
Penny tags along on Sheldon's first date; Wolowitz finds a new use f..
While Penny worries that dating Leonard has ruined her for normal gu..
Leonard tells Penny about how he met Sheldon for the first time...an..
Leonard and Sheldon compete for the attention of a famous female phy..
When Leonard and Penny aren't speaking, Sheldon goes to extremes to ..
A fight between Leonard and Penny threatens their relationship, whil..
Sheldon's friends come to his aid when his fear of public speaking s..
When the guys find a ring from "The Lord of the Rings" at a garage s..
Sheldon winds up in traffic court when he gets a ticket because of P..
Leonard can only bring one guest on a trip to see CERN's Large Hadro..
Sheldon's search for the answer to a physics problem leads him to wo..
A robbery of their apartment sees Leonard and Sheldon call on their ..
Leonard is aghast to find out a secret of Penny's: she believes in p..
Leonard's mother (Christine Baranski) visits, which pleases Sheldon ..
Sheldon attempts to help Penny understand Leonard's work, and Wolowi..
Barry Kripke embarrasses Sheldon on NPR, and the gang rallies to hel..
With Leonard, Howard and Raj away camping in the desert, an injured ..
A squabble between Leonard and Penny sees Sheldon playing mediator, ..
Sheldon teaches Leonard how to understand football while a kite-figh..
Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Pe..
Raj must find a new job or be sent back to India, but Sheldon has a ..
Howard takes Raj along to check out the Goth dating scene. Sheldon u..
Sheldon and Howard wager comic books over a cricket's species. Meanw..
Sheldon flees back to Texas in disgrace when he learns the guys tamp..
Leonard and Penny come to terms with their feelings for each other, ..
Things begin to look up for Leonard when Penny makes a surprising re..
Leonard and Koothrappali take a heartbroken Wolowitz to Las Vegas, l..
A fellow comic book enthusiast's hitting on Penny leads to Leonard a..
Penny feels threatened when another sexy woman moves into the apartm..
Penny's business selling hair products out of her apartment gets out..
The gang is thrilled when they learn Terminator: The Sarah Connor Ch..
Paintball leads to a squabble between Sheldon and Penny, as well as ..
Leonard suffers through a dreadful visit from his mother (Christine ..
Sheldon helps Penny with a financial crisis, but his solution leads ..
Sheldon creates a scientific procedure for making friends.
Penny's criticism of Wolowitz's romantic life pushes him into depres..
Penny informs Sheldon that she intends to give gifts to him and Leon..
Leonard's relationship with Stephanie is moving too fast for him, so..
Sheldon is overexuberant that Leonard finally has a girlfriend match..
A girl Wolowitz has a major crush on falls for Leonard.
When Sheldon bans Penny from the apartment for numerous minor infrac..
Sheldon, and his friends, are mystified when a younger grad student ..
An intervention is used to try to force Sheldon to overcome his fear..
Full of confidence following getting a paper published, Raj hits on ..
Sheldon creates a monster when he introduces Penny to online gaming.
Leonard begins dating Sheldon’s nemesis, Leslie Winkle, after seei..
Penny opens up to a reluctant Sheldon after a less-than-stellar firs..
Leonard comforts Penny after she breaks up with her boyfriend, again..
After finding out Leonard has never had a birthday party Penny decid..
When Sheldon's attractive twin sister Missy comes to visit the guys ..
Leonard buys a replica time machine online. As the boys move it into..
The guys decided to compete in a physics bowl but find Sheldon's sho..
Sheldon and Leonard look for a way to derail a 15-year-old physics p..
When Sheldon gets sick, Leonard and the boys know what's in store an..
After hearing Penny sing, Leonard lies to avoid seeing her perform, ..
When Sheldon and Leonard are invited to present their joint findings..
Koothrappali's parents want him to go out with another Indian woman ..
When Wolowitz hooks up with Penny's old friend, it ruins "Halo Night..
The guys are invited to Penny's Halloween costume party. During the ..
Leonard and his colleague Leslie spend the night together. But Lesli..
Sheldon's mother visits to get him out of the funk he's in after he ..
Leonard gets upset when he discovers that Penny is seeing a new guy,..
Penny is furious and more than a little freaked out with Leonard and..
A pair of brilliant theoretical physicists meet a woman who shows th..
The unreleased pilot of the Big Bang Theory featuring Leonard and Sh..