Summary: Mensa-fied best friends and roommates Leonard and Sheldon, physicists who work at the California Institute of Technology, may be able to tell everybody more than they want to know about quantum physics, but getting through most basic social situations, especially ones involving women, totally baffles them. How lucky, then, that babe-alicious waitress/aspiring actress Penny moves in next door. Frequently seen hanging out with Leonard and Sheldon are friends and fellow Caltech scientists Wolowitz and Koothrappali. Will worlds collide? Does Einstein theorize in the woods?
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S03, E02 (First Aired:
Penny and Leonard try to recover from an awkward hookup; Howard and Sheldon make a high-stakes bet.
S03, E03 (First Aired:
Howard and Raj hit a Goth nightclub to meet women; Sheldon tries chocolate-based behavior modification on Penny.
S03, E04 (First Aired:
Raj faces deportation if he does not find a job; Leonard and Penny deal with Howard as a third wheel.
S03, E05 (First Aired:
Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.
S03, E06 (First Aired:
Sheldon teaches Leonard how to understand football; a kite-fighting incident threatens Howard and Raj's friendship.
S03, E08 (First Aired:
Penny is forced to rely on Sheldon when she is injured while Howard, Leonard and Raj are away.
S03, E09 (First Aired:
After being humiliated on the radio, Sheldon vows to destroy Kripke; Wolowitz tries to not ruin his new relationship with Bernadette.
S09, E13 (First Aired:
After dealing with Sheldon while he was sick, Leonard, Penny and the gang attempt to treat themselves to a Sheldon-free weekend.
S03, E10 (First Aired:
Sheldon tries to help Penny understand Leonard's work; Wolowitz gets jealous when Leonard starts hanging out with his new girlfriend.
S03, E12 (First Aired:
Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.
S03, E13 (First Aired:
After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.
S03, E14 (First Aired:
Sheldon tries to figure out the answer to a physics problem by working with Penny.
S03, E15 (First Aired:
Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.
S03, E17 (First Aired:
When the guys buy a ring from ``The Lord of the Rings'' at a garage sale, the item threatens to tear them apart.
S03, E19 (First Aired:
Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.
S03, E20 (First Aired:
Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.
S03, E21 (First Aired:
Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.
S03, E22 (First Aired:
Leonard tells Penny about how he met Sheldon and what happened to the elevator.
S03, E23 (First Aired:
Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.
S04, E01 (First Aired:
Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.
S04, E02 (First Aired:
Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.
S04, E03 (First Aired:
When Sheldon searches for an alternative to human companionship, the guys become concerned.
S04, E04 (First Aired:
An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.
S04, E05 (First Aired:
Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.
S04, E08 (First Aired:
While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.
S04, E09 (First Aired:
Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.
S04, E10 (First Aired:
Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.
S04, E12 (First Aired:
Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.
S04, E13 (First Aired:
Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.
S04, E14 (First Aired:
Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.
S04, E16 (First Aired:
Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.
S04, E17 (First Aired:
Sheldon is upset when he realizes Leonard is the center of their group of friends.
S04, E18 (First Aired:
Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.
S09, E14 (First Aired:
Sheldon's excitement about his Meemaw's visit fades when she butts heads with Amy; Raj questions his relationship with Emily after meeting someone new.
S04, E20 (First Aired:
Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.
S04, E22 (First Aired:
Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.
S04, E23 (First Aired:
Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.
S04, E24 (First Aired:
Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.
S05, E01 (First Aired:
Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.
S05, E02 (First Aired:
Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.
S05, E03 (First Aired:
Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.
S05, E04 (First Aired:
Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.
S05, E05 (First Aired:
Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.
S05, E06 (First Aired:
Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.