5 seasons available
Sheldon and Amy await big news.
Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.
Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.
When Sheldon searches for an alternative to human companionship, the guys become concerned.
An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.
Sheldon tries to figure out the answer to a physics problem by working with Penny.
Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.
Sheldon ends up in traffic court after getting a ticket because of Penny.
When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.
Sheldon's stage fright stands between him and a coveted award.
Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.
Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.
Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.
Leonard tells Penny about how he met Sheldon and what happened to the elevator.
Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.
Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.
After seeing Penny with a handsome new guy, Leonard rushes into a rebound relationship with Sheldon's nemesis, Leslie Winkle.
Sheldon creates a monster when he introduces Penny to online gaming.
Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.
Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.
Sheldon and the gang are confused when a young grad student is attracted to him.
When Sheldon bans Penny from the apartment for a series of petty infractions, Penny vows to get revenge.
Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.
Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.
Leonard asks Penny for advice when his new relationship starts moving too fast.
Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.
When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting-robot competition.
Sheldon develops a scientific procedure for making friends; Kripke controls a new supercomputer.
Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.
Leonard and Penny are drawn together after a disastrous visit from Leonard's mother (Christine Baranski).
A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.
Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is aboard the train they are taking to San Francisco.
Penny's home business turns into a complete nightmare when Sheldon takes over.
Penny develops a rivalry with a sexy new female neighbor who threatens her position as queen bee of the building.
Wolowitz and Leonard decide to check out a local bar on Ladies' Night.
Koothrappali and Leonard take Wolowitz to Las Vegas; Sheldon is forced to bunk with Penny when he gets locked out of his apartment.
Penny makes a surprising revelation about Leonard while on her date with Stuart; Wolowitz finds a critical design flaw in his NASA project.
While Leonard prepares for a three-month science expedition, he and Penny re-evaluate their feelings for each other.
Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.
Leonard volunteers to sign for a package, hoping to make a good impression on Penny.
Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.
Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.
Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).
Leonard, Sheldon, Wolowitz and Koothrappali attend Penny's Halloween party.
Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.
On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.
Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.
Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.
Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.
Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.
When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.
Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.
Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.
Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.
When Leonard finally works up the courage to ask Penny out on a date, they each turn to Sheldon for advice.