Pilot When Leonard and Sheldon meet new neighbor Penny, Leonard is excited, but Sheldon is less enthusiastic for he feels his friend is only chasing a dream he'll never catch.
The Big Bran Hypothesis Leonard volunteers to sign for a package, hoping to make a good impression on Penny. When he enlists the help of his obsessive-compulsive roommate, Sheldon, his attempt at chivalry goes horribly awry.
The Fuzzy Boots Corollary Leonard is bummed to learn that his crush, Penny, is seeing someone, so encouraged by his friends and fellow scientists, Leonard actually summons the nerve to ask a woman out on a date.
The Luminous Fish Effect When Sheldon gets fired, he explores 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.
The Hamburger Postulate After sensing his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle.
The Middle Earth Paradigm Leonard, Sheldon, Wolowitz and Koothrappali undertake a challenging and risky experiment-attending the Halloween party being thrown by their hot neighbor, Penny.
The Dumpling Paradox When Wolowitz seduces Penny's friend and takes over her apartment, Penny sleeps on Leonard and Sheldon's couch. With Wolowitz preoccupied, the guys discover they are without a fourth member of their group and in desperation, they ask Penny to join their Halo team.
The Grasshopper Experiment Koothrappali is overwhelmed after his parents arrange a blind date, but he discovers he actually can talk to the opposite sex after a few drinks; however, complications set in when his beautiful date is more interested in Sheldon.
The Cooper-Hofstadter Polarization Sheldon and Leonard are asked to a physics conference to present their work together, but that leads to a feud because Sheldon's too arrogant to share the honor. Penny does her best to mediate, but only makes things worse.
The Loobenfeld Decay After hearing Penny sing, Leonard lies to avoid seeing her perform, but Sheldon takes it one step further with a more elaborate lie that leads to the appearance of his non-existent cousin.
The Pancake Batter Anomaly When Sheldon gets sick, Leonard and the boys know what's in store and avoid him like the plague, leaving an unsuspecting Penny to nurse the world's worst patient back to health.
The Jerusalem Duality When Leonard and Sheldon meet a 15-year-old physics prodigy, Sheldon is distraught that this boy genius is younger and smarter, so in an attempt to restore his sense of purpose, the boys come up with a solution to derail Dennis' research.
The Bat Jar Conjecture Since Sheldon's only focus is to prove his mental superiority while preparing for the Physics Bowl, the guys kick him off the team and enlist his nemesis Leslie Winkle.
The Nerdvana Annihilation 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 Shiksa Indeterminancy When Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Leonard devises a plan to eliminate his rivals, however, it backfires when Sheldon declares he will decide whom his sister dates.
The Peanut Reaction When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party, but is sidetracked by Sheldon who unexpectedly gets to live out one of his greatest fantasies at an electronics store.
The Tangerine Factor When Leonard asks Penny out on a date and she says yes, they each seek the "wisdom" of reluctant advisor, Sheldon.