Criminal Minds : Seasons 1 - 6

Criminal Minds is an American police procedural drama that premiered September 22, 2005 on CBS. The series follows a team of profilers from the FBI's Behavioral Analysis Unit (BAU) based in Quantico, Virginia. The BAU is part of the FBI National Center for the Analysis of Violent Crime. Criminal Minds differs from many procedural dramas by focusing on the criminal rather than the crime itself. The show is produced by The Mark Gordon Company in association with CBS Television Studios and ABC Studios. The original title for Criminal Minds was Quantico, and the pilot was filmed in Vancouver. In the Quantico script, Jason Gideon was named Jason Donovan.
Initially, the series centered on Jason Gideon (Mandy Patinkin), Aaron Hotchner (Thomas Gibson), and the rest of the Behavioral Analysis Unit, hereafter referred to as the BAU team. For the first season, that team is composed of Elle Greenaway (Lola Glaudini), Derek Morgan (Shemar Moore), Dr. Spencer Reid (Matthew Gray Gubler), Jennifer "JJ" Jareau, (AJ Cook), and Penelope Garcia (Kirsten Vangsness). When the series premiered, Vangsness was not in the regular cast, appearing instead as a guest star.
During the second season, Greenaway left after the sixth episode and is replaced in the ninth episode of that season by Emily Prentiss (Paget Brewster). At the start of the third season, Gideon departs after the second episode and is replaced several episodes later by David Rossi (Joe Mantegna). During the sixth season, JJ leaves after the second episode. A new character Ashley Seaver (Rachel Nichols) is introduced in Season 6. Also, later on in the sixth season, Prentiss leaves the show. AJ Cook returned to the show to participate in Brewster's final episode, billed as a "special guest star".
For the seventh season, it was announced that Cook signed a two year contract to return as a series regular at the end of the sixth season and for the beginning of the seventh season and it was also announced that Brewster would actually be returning as Prentiss as a series regular for season seven. Nichols' contract was not extended for season seven, meaning she departed the cast. Moore's and Gibson's contracts were both renewed and their salaries were both raised.