Episode Guide :: Season 4
The Big Bang Theory's fourth season focuses on character growth as Sheldon enters a platonic relationship with Amy, Howard restarts his romance with Bernadette, and Leonard starts a serious relationship with Raj's sister Priya.
As Sheldon becomes comfortable spending more time with Amy, his "girl who is a friend but not a girlfriend", starts to spend more time with the group and forms friendship with Penny. Howard's girlfriend Bernadette also becomes a part of the group. After dating for a few months, Howard and Bernadette get engaged after he proposes.
Leonard enters a long-term relationship with Priya, Raj's sister, after she moves to Pasadena. Seeing Leonard with another women, Penny begins to regret breaking up with him. In the season finale, after a night of drinking, Raj and Penny get very close.
The Big Bang Theory's fourth season contained twenty-four episodes aired between September 23, 2010 and May 19, 2011. For its third season, The Big Bang Theory moved to Thursdays at 8:00 on CBS, to form a new comedy block. Although the show continued to perform well in the ratings, it fell somewhat from the third season. The new timeslot lacked the strong lead-in the show had on Mondays, with TV's then-#1 sitcom Two and a Half Men, and suffered fewer people watching TV at the earlier time. Kaley Cuoco was absent from two episodes during the season, due to a broken leg from horseback-riding accident.