Leonard volunteers to sign for a package in an attempt to make a good impression on Penny, but when ...

Leonard asks a woman out after he finds out that Penny is seeing someone.

Sheldon's getting fired forces him to explore what life has to offer outside physics, leaving Leonar...

Fearing he's wasting his time on Penny, Leonard ends up making a connection with Leslie.

Penny hosts a Halloween party, putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new te...

With Wolowitz AWOL with one of her friends, Penny's recruited to fill in for him on the guys' Halo t...

Raj's parents set him up on a blind date, but just when he discovers he can talk to her, she shows i...

When they're invited to present at a physics conference, Sheldon's reluctance to share the credit le...

Leonard and Sheldon each lie to avoid seeing Penny's concert, but Sheldon's is a bit too complicated...

With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed b...

With Sheldon rattled over meeting Dennis, a 15-year-old physicist who's smarter than he, Leonard hel...

Sheldon finds himself booted from the gang's Physics Bowl team and replaced with Leslie, so he forms...

When delivery of another collectible leads to Penny's lashing out at Leonard, he decides it's time t...

The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed...

Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store ...

Penny's break-up spurs Leonard to summon the courage to ask her out, and each goes to Sheldon for ad...