The third season of the American sitcom The Big Bang Theory was originally aired on CBS from September 21, 2009 to May 24, 2010 with 23 episodes.It received higher ratings than the previous two seasons with over 15 million viewers.After prodding by Leonard, a reluctant Penny sets Howard with her friend Bernadette, though they find they have little in common.
When Penny announces that her guitarist friend, who she dated twice, is going to sleep on her couch for the next few days, Leonard is upset that she didn't ask him first.
Sheldon is upset by reminders of his quarrelling parents as Leonard and Penny fight, Raj argues with his parents and Howard argues with his mother.
After she explains this to Leonard, the two agree to do so, but they find that neither wants to and have sex again.
Penny's bed in her apartment breaks, forcing her to sleep at Leonard and Sheldon's apartment for a few days.
Season three started three months after the end of season two when the guys left for the North Pole.
The third season saw the first appearances of future main cast members Melissa Rauch as Bernadette Rostenkowski in “The Creepy Candy Coating Corollary” and Mayim Bialik as Dr.Sheldon, despite never having driven a car before, is forced to drive Penny to the hospital after she slips in the shower.Leonard, Raj and Howard go on a camping trip to watch the Leonid meteor shower, but all succumb to the effects of "magic" cookies given to them by Deadhead campers nearby, causing them to blurt out weird secrets including Howard losing his virginity to his second cousin.Raj's research on trans-Neptunian objects comes to a dead end and he faces deportation to India unless he gets a new job. Howard tries to hang out with Leonard and Penny, but intrudes into their relationship.Howard reminds Leonard of their girlfriend pact: one of the two men (Leonard) who has a girlfriend (Penny) must have her set the other man (Howard) up on a date with her friend.Sheldon tries to condition Penny, rewarding with chocolate what he considers to be "correct" behavior.Howard and Raj pretend to be goths to try to meet girls at a goth club, but chicken out when the girls persuade them to get tattoos. Eventually, Sheldon apologises to Raj, conceding that his theory is correct but refusing to give up on his own.When Leonard arrives in Texas, it is Mary who convinces Sheldon to forgive him by disagreeing with his views on evolution.Leonard and Penny then finally have sex, but concede that things are now weird between them.Leonard and Penny vacillate between friendship and a romantic relationship, struggling to resolve the awkwardness.In an attempt to feel comfortable and talk about a solution, they end up getting drunk in her apartment and throwing up all night.