The Big Bang Theory

After her first date with Leonard (series star JOHNNY GALECKI) goes awry, Penny (series star KALEY CUOCO) finds an unwilling confidante in Leonard's anti-social roommate, Sheldon (series star JIM PARSONS). An embarrassing secret threatens to derail their budding romance on the second season premiere.

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 st ar TRAVIS SCHULDT Scrubs), he enters into a rebound relationship withSheldon's nemesis, Leslie Winkle (series regular SARA GILBERT).

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

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.

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

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

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.

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

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

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

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

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.

Socially awkward Sheldon develops a scientific procedure for making friends.

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).

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

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.

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: The Sarah Connor Chronicles") is onboard. Nobel Laureate for Physics and "Big Bang" theorist, Dr. George Smoot also makes a cameo.

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

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."

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.

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

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.

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.