Set in Pasadena, California, the show is about two Caltech prodigies in their 20s, one an experimental physicist (Leonard Hofstadter) and the other a theoretical physicist (Sheldon Cooper), who live across the hall from an attractive blonde waitress with show-biz aspirations (Penny). Leonard and Sheldon's 'geekiness' and sheer intellect are contrasted for comic effect with Penny's social skills and common sense. Two equally geeky friends of theirs, Howard and Rajesh, are also main characters.

Source: Wikipedia.org