The Big Bang Theory, Season 1

Meet two brainiacs with a lot to learn. Leonard and Sheldon can tell their quarks from their quantum physics, but have no clue how women add up. Leave it to their pretty new neighbor, just off a messy breakup, to teach them a thing or two.

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.

When Leonard sees Penny kissing a guy in front of her apartment door he is devastated. The guys convince him to ask someone out at work, but when he tries and is brutally turned down by a geeky girl, he is even more depressed.

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").

After sensing that his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle (recurring guest star Sara Gilbert). The one-night stand throws Leonard and Sheldon deep into uncharted social waters.

The socially stunted guys are nervous when Penny invites them to a party she's hosting.

When Wolowitz seduces Penny's friend and ends up sleeping with her in Penny's apartment, Penny sleeps on Leonard and Sheldon's couch.

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.

Sheldon and Leonard are invited to present their joint findings at a physics conference, but Sheldon refuses.

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.

Sheldon gets sick and Penny has to deal with him.

When Leonard and Sheldon meet a teenage physics prodigy, Sheldon is distraught that the boy genius is younger and smarter, and crafts a plan to derail the young prodigy's research.

The guys kick Sheldon off the team for the Physics Bowl and enlist his nemesis Leslie Winkle (recurring guest star Sara Gilbert) to take his place.

When the guys buy a time-machine prop from a classic movie, Penny's reaction forces Leonard to take a hard look at his life.

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 plan backfires, however, when Sheldon declares he will decide whom his sister dates.

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.

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.