Pilot

Season 1, Episode 1 Unrated CC HD CC SD

In the series premiere, when Leonard and Sheldon meet Penny, Leonard is immediately interested in her. But Sheldon feels his friend is chasing a dream he'll never catch.

The Big Bran Hypothesis

Season 1, Episode 2 Unrated CC HD CC SD

After Leonard tries to do a favor for Penny, Sheldon ruins the plan. Leonard volunteers to sign for a package, hoping to make a good impression on Penny. However, when he involves his obsessive-compulsive roommate, Leonard sees his attempt at chivalry go horribly awry.

The Fuzzy Boots Corollary

Season 1, Episode 3 Unrated CC HD CC SD

Two brainy best friends could tell you anything you want to know about quantum physics but when it comes to dealing with everyday life here on Earth, they're lost in the cosmos.

The Luminous Fish Effect

Season 1, Episode 4 Unrated CC HD CC SD

After being fired from his job, Sheldon attempts to explore the "dreadful" 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, Mary (LAURIE METCALF - "Roseanne").

The Hamburger Postulate

Season 1, Episode 5 Unrated CC HD CC SD

After sensing that his pursuit of Penny isn't going anywhere, Leonard agrees to unexpected sexual encounter with fellow scientist Leslie Winkle (recurring guest star SARA GILBERT).

The Middle Earth Paradigm

Season 1, Episode 6 Unrated CC HD CC SD

The socially stunted guys are nervous when Penny invites them to a party she's hosting. But they are ecstatic to find out that it's a Halloween party and enthusiastically don their respective nerdy costumes, which unfortunately fail to impress Penny's brutish ex-boyfriend. Afterwards, Koothrappali experiences the unexpected with a partygoer, Cheryl (ERIN ALLIN).

The Dumpling Paradox

Season 1, Episode 7 Unrated CC HD CC SD

When Wolowitz seduces Penny's friend and ends up sleeping with her in Penny's apartment, Penny sleeps on Leonard and Sheldon's couch. Meanwhile, with Wolowitz occupied, the guys discover that they are without a fourth member of their group. In desperation, they ask Penny to join one of their two-person Halo teams.

The Grasshopper Experiment

Season 1, Episode 8 Unrated CC HD CC SD

Koothrappali becomes overwhelmed when his parents arrange a blind date for him, but he discovers he actually can talk to a member of the opposite sex after a few drinks. However, complications arise when his beautiful date shows more interest in Sheldon.

The Cooper-Hofstadter Polarization

Season 1, Episode 9 Unrated CC HD CC SD

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

The Loobenfeld Decay

Season 1, Episode 10 Unrated CC HD CC SD

After hearing Penny sing, Leonard lies to avoid seeing her perform. Sheldon goes one step further with a more elaborate lie, leading to the appearance of his nonexistent cousin. D.J. QUALLS ("Road Trip") guest stars.

The Pancake Batter Anomaly

Season 1, Episode 11 Unrated CC HD CC SD

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

The Jerusalem Duality

Season 1, Episode 12 Unrated CC HD CC SD

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

The Bat Jar Conjecture

Season 1, Episode 13 Unrated CC HD CC SD

The guys decide to compete in the university's Physics Bowl, but since Sheldon's only focus is to prove his mental superiority, the guys kick him off the team. To take his spot, they enlist his nemesis Leslie Winkle (recurring guest star SARA GILBERT).

The Nerdvana Annihilation

Season 1, Episode 14 Unrated CC HD CC SD

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."

The Porkchop Indeterminacy

Season 1, Episode 15 Unrated CC HD CC SD

Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Missy (guest star COURTNEY HENGGELER), and Leonard devises a plan to eliminate his rivals.

The Peanut Reaction

Season 1, Episode 16 Unrated CC HD CC SD

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

The Tangerine Factor

Season 1, Episode 17 Unrated CC HD CC SD

When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor -- Sheldon.

The Bad Fish Paradigm

Season 1, Episode 18 Unrated CC HD CC SD

In the second season premiere, after her first date with Leonard goes awry, Penny finds an unwilling confidant in Leonard's anti-social roommate, Sheldon.

The Codpiece Topology

Season 1, Episode 19 Unrated CC HD CC SD

Penny and Leonard compete to see who will be the first to move on after their breakup. When Leonard sees Penny with a handsome new guy (guest star TRAVIS SCHULDT Scrubs), he enters into a rebound relationship with Sheldon's nemesis, Leslie Winkle (series regular SARA GILBERT).

The Barbarian Sublimation

Season 1, Episode 20 Unrated CC HD CC SD

Sheldon creates a monster when he introduces Penny to the world of online gaming. Especially when her addiction wreaks havoc on his life.

The Griffin Equivalency

Season 1, Episode 21 Unrated CC HD CC SD

Rajs ego puts all of his friendships in jeopardy when he gets an inflated sense of self. Newly famous because of an article in a magazine, Raj (series regular KUNAL NAYYAR) makes a disastrous play for Leonards longtime crush, Penny.

The Euclid Alternative

Season 1, Episode 22 Unrated CC HD CC SD

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

The Cooper-Nowitzki Theorem

Season 1, Episode 23 Unrated CC HD CC SD

A young grad students attraction to Sheldon confuses everyone including Sheldon himself.

The Panty Pinata Polarization

Season 1, Episode 24 Unrated CC HD CC SD

Sheldon and Penny engage in a battle of wills as Penny vows to get revenge on Sheldon when he bans her from the apartment for a series of petty infractions.

The Lizard-Spock Expansion

Season 1, Episode 25 Unrated CC HD CC SD

Wolowitz (series regular SIMON HELBERG) thinks he's found the love of his life (guest star SARA RUE) until she meets Leonard.

The White Asparagus Triangulation

Season 1, Episode 26 Unrated CC HD CC SD

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

The Vartabedian Conundrum

Season 1, Episode 27 Unrated CC HD CC SD

Leonard just can't say no. When his relationship with new girlfriend, Stephanie starts moving too fast, Leonard turns to Penny for advice.

The Bath Item Gift Hypothesis

Season 1, Episode 28 Unrated CC HD CC SD

Leonards handsome colleague starts dating Penny. And Leonards friends are being tormented by Sheldon's obsession with gift-giving etiquette.

The Killer Robot Instability

Season 1, Episode 29 Unrated CC HD CC SD

When Pennys comment about Wolowitzs love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting robot competition.

The Friendship Algorithm

Season 1, Episode 30 Unrated CC HD CC SD

Socially awkward Sheldon develops a scientific procedure for making friends.

The Financial Permeability

Season 1, Episode 31 Unrated CC HD CC SD

Sheldon's "simple" solution to Penny's financial problem leads to a confrontation between Leonard and Penny's hulking ex-boyfriend, Kurt (guest star BRIAN PATRICK WADE).

The Maternal Capacitance

Season 1, Episode 32 Unrated CC HD CC SD

A disastrous visit from Mrs. Hofstadter (special guest star CHRISTINE BARANSKI) brings Leonard and Penny closer together.

The Cushion Saturation

Season 1, Episode 33 Unrated CC HD CC SD

A paintball game has surprising consequences for Leonard and his friends when it leads to a fight between Penny and Sheldon – and romance for Wolowitz and Leslie.

The Terminator Decoupling

Season 1, Episode 34 Unrated CC HD CC SD

A train trip to San Francisco takes a major detour when Leonard, Sheldon, Wolowitz and Raj discover that beautiful sci-fi actress SUMMER GLAU ("Terminator") is onboard.

The Work Song Nanocluster

Season 1, Episode 35 Unrated CC HD CC SD

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

The Dead Hooker Juxtaposition

Season 1, Episode 36 Unrated CC HD CC SD

There’s a new queen bee in the building! Penny develops a rivalry with a sexy female neighbor moves in to the building and threatens to become the “new Penny.”

The Hofstadter Isotope

Season 1, Episode 37 Unrated CC HD CC SD

While Stuart (guest star KEVIN SUSSMAN), 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.

The Vegas Renormalization

Season 1, Episode 38 Unrated CC HD CC SD

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

The Classified Materials Turbulence

Season 1, Episode 39 Unrated CC HD CC SD

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

The Monopolar Expedition

Season 1, Episode 40 Unrated CC HD CC SD

On the second season finale, Leonard and Penny reconsider their feelings for one another. When Leonard and his friends decide to spend the summer working – at the North Pole – Penny is conflicted.

The Electric Can Opener Fluctuation

Season 1, Episode 41 Unrated CC HD CC SD

On the third season premiere, Sheldon (series star JIM PARSONS) flees back to Texas in disgrace when he learns that the guys tampered with his arctic expedition data – forcing his friends to follow him, and threatening Leonard’s (series star JOHNNY GALECKI) hopes for a romantic encounter with Penny (series star KALEY CUOCO).

The Jiminy Conjecture

Season 1, Episode 42 Unrated CC HD CC SD

Leonard and Penny struggle to recover from an awkward first hookup, while Sheldon and Howard (SIMON HELBERG) stake their best comic books on a bet to determine an insect species.

The Gothowitz Deviation

Season 1, Episode 43 Unrated CC HD CC SD

Howard and Raj (series star KUNAL NAYYAR) visit a Goth nightclub to pick up women, while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

The Pirate Solution

Season 1, Episode 44 Unrated CC HD CC SD

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

The Creepy Candy Coating Corollary

Season 1, Episode 45 Unrated CC HD CC SD

While Sheldon settles a score with his nemesis, Star Trek’s WIL WHEATON (guest starring as himself), Wolowitz begs Leonard to get Penny to set him up with one of her friends.

The Cornhusker Vortex

Season 1, Episode 46 Unrated CC HD CC SD

Leonard learns about football from an unlikely tutor.

The Guitarist Amplification

Season 1, Episode 47 Unrated CC HD CC SD

Sheldon plays the peacemaker when an argument between Leonard and Penny proves “inconvenient” to him.

The Adhesive Duck Deficiency

Season 1, Episode 48 Unrated CC HD CC SD

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

The Vengeance Formulation

Season 1, Episode 49 Unrated CC HD CC SD

After he's humiliated on NPR, Sheldon vows to destroy Kripke, while, Wolowitz tries not to destroy his new relationship with Bernadette. KATEE SACKHOFF guest stars.

The Gorilla Experiment

Season 1, Episode 50 Unrated CC HD CC SD

Sheldon takes on his greatest challenge when he attempts to help Penny understand physics, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

The Maternal Congruence

Season 1, Episode 51 Unrated CC HD CC SD

A visit from Leonard’s mother (guest star CHRISTINE BARANSKI) delights Sheldon and horrifies Leonard.

The Psychic Vortex

Season 1, Episode 52 Unrated CC HD CC SD

While Sheldon and Koothrappali attend a university mixer, Leonard is upset to discover that Penny believes in psychics. DANICA McKELLAR (The Wonder Years) guest stars as the object of Raj’s attraction.

The Bozeman Reaction

Season 1, Episode 53 Unrated CC HD CC SD

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

The Einstein Approximation

Season 1, Episode 54 Unrated CC HD CC SD

Suffering from a case of “physicist’s block,” Sheldon’s search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

The Large Hadron Collision

Season 1, Episode 55 Unrated CC HD CC SD

It’s Valentine’s Day, and Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland. Will it be Sheldon or Penny?

The Excelsior Acquisition

Season 1, Episode 56 Unrated CC HD CC SD

Sheldon misses his chance to meet comic book legend STAN LEE (as himself) when he winds up in traffic court after he gets a ticket because of Penny.

The Precious Fragmentation

Season 1, Episode 57 Unrated CC HD CC SD

When the guys find a rare movie prop ring from The Lord of the Rings at a garage sale, it threatens to tear them apart – forcing them to choose the ring or their friendship.

The Pants Alternative

Season 1, Episode 58 Unrated CC HD CC SD

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

The Wheaton Recurrence

Season 1, Episode 59 Unrated CC HD CC SD

A fight between Leonard and Penny threatens their relationship, while Sheldon battles WIL WHEATON (guest starring as Himself) in bowling.

The Spaghetti Catalyst

Season 1, Episode 60 Unrated CC HD CC SD

When Leonard and Penny aren’t speaking, Sheldon goes to extremes to keep them both happy and gets caught in a lie.

The Plimpton Stimulation

Season 1, Episode 61 Unrated CC HD CC SD

Leonard and Sheldon compete for the attention of a famous female physicist – Dr. Elizabeth Plimpton (guest star JUDY GREER).

The Staircase Implementation

Season 1, Episode 62 Unrated CC HD CC SD

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

The Lunar Excitation

Season 1, Episode 63 Unrated CC HD CC SD

In the third season finale, Wolowitz and Koothrappali search for Sheldon's perfect match online – and find Sheldon’s ideal woman (guest star MAYIM BIALIK). Meanwhile, Penny worries that dating Leonard has ruined her for normal guys.

The Robotic Manipulation

Season 1, Episode 64 Unrated CC HD CC SD

On the fourth season premiere, Penny (series star KALEY CUOCO) finds herself along for the ride on Sheldon's (series star JIM PARSONS) first date ever. Meanwhile, Wolowitz (series star SIMON HELBERG) finds a new use for a robotic arm. MAYIM BIALIK guest stars as Sheldon’s date, Amy Fowler.

The Cruciferous Vegetable Amplification

Season 1, Episode 65 Unrated CC HD CC SD

When Sheldon realizes he won’t live long enough to download his consciousness into a robot body, he attempts to extend his lifespan. Apple Co-Founder STEVE WOZNIAK guest stars as Himself.

The Zazzy Substitution

Season 1, Episode 66 Unrated CC HD CC SD

The guys are concerned as Sheldon searches for an alternative to human companionship after he and Amy (MAYIM BIALIK) break up. LAURIE METCALF reprises her role as Sheldon’s mother.

The Hot Troll Deviation

Season 1, Episode 67 Unrated CC HD CC SD

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work. Battlestar Galactica’s KATEE SACKHOFF and Star Trek’s GEORGE TAKEI guest star as themselves as Wolowitz's love gurus. MELISSA RAUCH reprises her role as Howard’s girlfriend, Bernadette.

The Desperation Emanation

Season 1, Episode 68 Unrated CC HD CC SD

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

The Irish Pub Formulation

Season 1, Episode 69 Unrated CC HD CC SD

A visit from Raj’s sister (guest star AARTI MANKAD) creates tension among the guys – especially when Leonard keeps an affair secret from Sheldon, Howard and Raj.

The Apology Insufficiency

Season 1, Episode 70 Unrated CC HD CC SD

When an FBI agent (guest star ELIZA DUSHKU) interviews the guys for Wolowitz’s security clearance, Sheldon’s answers during the screening, put Wolowitz’s clearance in jeopardy.

The 21-Second Excitation

Season 1, Episode 71 Unrated CC HD CC SD

When the guys camp in line for a screening, their plans are thwarted by Sheldon’s greatest nemesis, WIL WHEATON (guest starring as himself). Meanwhile, Penny and Bernadette invite Amy to her first slumber party.

The Boyfriend Complexity

Season 1, Episode 72 Unrated CC HD CC SD

Penny asks Leonard to lie to her father, Wyatt (guest star KEITH CARRADINE), while Howard, Raj and Bernadette pull an all-nighter at a telescope.

The Alien Parasite Hypothesis

Season 1, Episode 73 Unrated CC HD CC SD

Amy finds she has sexual feelings for Penny's ex, Zack (guest star BRIAN THOMAS SMITH) while Koothrappali and Wolowitz try to prove who would be the better superhero.

The Justice League Recombination

Season 1, Episode 74 Unrated CC HD CC SD

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

The Bus Pants Utilization

Season 1, Episode 75 Unrated CC HD CC SD

Leonard’s idea for a smartphone app derails his friendship with Sheldon as they fight for control of the project.

The Love Car Displacement

Season 1, Episode 76 Unrated CC HD CC SD

Tension runs high when everyone is staying at the same hotel for a science event and Bernadette runs into her ex-boyfriend (guest star RICK FOX, three-time NBA champion with the Los Angeles Lakers).

The Thespian Catalyst

Season 1, Episode 77 Unrated CC HD CC SD

Sheldon wants Penny to give him acting lessons, hoping that they will help him become a better teacher. Meanwhile, Koothrappali fantasizes about his best friend's girlfriend.

The Benefactor Factor

Season 1, Episode 78 Unrated CC HD CC SD

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science. JESSICA WALTER (Arrested Development) guest stars as the widowed benefactress and JOSHUA MALINA (The West Wing) guest stars as the University President.

The Cohabitation Formulation

Season 1, Episode 79 Unrated CC HD CC SD

As Wolowitz contemplates taking things with Bernadette to the next level, he must choose between his girlfriend and his mother. Meanwhile, Leonard rekindles his relationship with Raj’s sister, Priya.

The Toast Derivation

Season 1, Episode 80 Unrated CC HD CC SD

When the gang starts hanging out at Raj’s and Sheldon realizes it’s actually Leonard who is the center of their social group, Sheldon decides to get a new group of friends.

The Prestidigitation Approximation

Season 1, Episode 81 Unrated CC HD CC SD

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

The Zarnecki Incursion

Season 1, Episode 82 Unrated CC HD CC SD

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

The Herb Garden Germination

Season 1, Episode 83 Unrated CC HD CC SD

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

The Agreement Dissection

Season 1, Episode 84 Unrated CC HD CC SD

Priya uses her lawyer skills to pick apart the roommate agreement…and put Sheldon in his place. Meanwhile, the girls take Sheldon dancing.

The Wildebeest Implementation

Season 1, Episode 85 Unrated CC HD CC SD

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

The Engagement Reaction

Season 1, Episode 86 Unrated CC HD CC SD

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

The Roomate Transmorgrification

Season 1, Episode 87 Unrated CC HD CC SD

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, on the fourth season finale.

The Skank Reflex Analysis

Season 1, Episode 88 Unrated CC HD CC SD

The fifth season premiere picks up where the fourth season finale left off as the gang deals with the aftermath of Penny and Raj’s night together. While Penny worries that she’s screwed things up permanently with her friends, Sheldon takes command of the paintball team. Emmy® nominee CHRISTINE BARANSKI (The Good Wife) reprises her role as Leonard’s emotionally distant mother.

The Infestation Hypothesis

Season 1, Episode 89 Unrated CC HD CC SD

A battle of wills between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya (recurring guest star AARTI MANN), who has moved back to India.

The Pulled Groin Extrapolation

Season 1, Episode 90 Unrated CC HD CC SD

Leonard attends a co-worker’s wedding as Amy’s date. Meanwhile, Howard tries to convince Bernadette to live with his mom after they get married by suggesting a trial run with the two of them staying with his mom over the weekend.

The Wiggly Finger Catalyst

Season 1, Episode 91 Unrated CC HD CC SD

When Raj is upset he’s the only one of the four guys who is not in a relationship, Penny sets out to find the perfect date, introducing him to Emily (guest star KATIE LeCLERC – Switched at Birth) a girl he can actually talk to!

The Russian Rocket Reaction

Season 1, Episode 92 Unrated CC HD CC SD

Sheldon’s old nemesis, WIL WHEATON (guest starring as Himself), returns and invites everyone to a housewarming party. Sheldon threatens to “defriend” Leonard if he attends. But when he hears that BRENT SPINER (guest starring as Himself), the actor who played Commander Data, will be there, Sheldon decides to go to the party after all… only to discover new levels of treachery. Meanwhile, Howard gets an out-of-this-world opportunity that Bernadette reacts to strongly.

The Rhinitis Revelation

Season 1, Episode 93 Unrated CC HD CC SD

Sheldon's mother, Mary Cooper (Laurie Metcalf), comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.

The Good Guy Fluctuation

Season 1, Episode 94 Unrated CC HD CC SD

A cute comic book artist (guest star COURTNEY FORD) puts Leonard’s relationship with Priya to the test; while Sheldon, getting into the spirit of Halloween, tries to scare the guys.

The Isolation Permutation

Season 1, Episode 95 Unrated CC HD CC SD

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

The Ornithophobia Diffusion

Season 1, Episode 96 Unrated CC HD CC SD

Can friends with benefits still be friends without? Leonard and Penny try hanging out alone, while Sheldon must overcome his fear of birds.

The Flaming Spittoon Acquisition

Season 1, Episode 97 Unrated CC HD CC SD