What is the name of the restaurant where the guys hang out in The Big Bang Theory?

The restaurant where the guys hang out in The Big Bang Theory is The Cheesecake Factory.

Penny works there as a waitress for much of the early series, and Leonard, Sheldon, Howard, and Raj regularly visit her during their meals. The restaurant becomes one of the show's recurring social locations, especially because it gives the characters another setting beyond Leonard and Sheldon's apartment, Caltech, and the comic-book store.

The Cheesecake Factory first appears as the gang's dining destination in “The Hamburger Postulate,” the fifth episode of Season 1. Penny's job also connects the restaurant to several storylines: she struggles to balance waitressing with acting, and Bernadette later works there while pursuing her graduate studies. Penny eventually leaves the restaurant to focus more seriously on acting.

A common mix-up is that the group eats many different meals elsewhere, including Chinese and Thai takeout, and they have recurring food routines such as pizza night. However, the named restaurant most closely associated with the guys' regular outings—and the place where Penny works—is The Cheesecake Factory, not Olive Garden, Chili's, or Applebee's.