Throughout its run, the series was generally led by four primary cast members (three in season 5), who were credited by their first names. Their storylines were largely developed by a number of supporting cast members. It originally focused on Lauren Conrad, who appeared in its predecessor, as she pursued a career in the fashion industry. It additionally placed emphasis on her housemate Heidi Montag and their friends Audrina Patridge and Whitney Port. Conrad's friend Lo Bosworth and Montag's boyfriend Spencer Pratt developed major positions as part of the supporting cast in the second season, while his sister Stephanie Pratt was added in the third. After moving to New York City, Port left the series upon the conclusion of the fourth season to launch her own spin-off The City.[5]
Looking to pursue other career opportunities, Conrad left the series halfway through the fifth season, and was subsequently replaced by fellow Laguna Beach: The Real Orange County cast member Kristin Cavallari.[6] Bosworth and the female Pratt joined Cavallari and Patridge as primary cast members in the sixth and final season, while Montag and her husband Pratt were removed from the show after four episodes.
^Bosworth is initially credited onscreen as "Lauren's friend" (seasons 2–5), "Audrina's friend" (season 5), then just her first name, before being added to the opening credits from "Put on a Happy Face" (ep. 6.1).
^Pratt is credited onscreen as "Spencer's sister", before being added to the opening credits from "A New Bird" (ep. 6.5).
^"Put On A Happy Face". The Hills. Season 6. Episode 1. April 27, 2010. MTV. Archived from the original on May 1, 2010. Retrieved July 11, 2013.
^ abc"Rolling With The Enemy". The Hills. Season 3. Episode 5. September 3, 2007. MTV. Archived from the original on November 2, 2013. Retrieved July 11, 2013.
^"A Change Of Plans". The Hills. Season 1. Episode 2. June 7, 2006. MTV. Archived from the original on October 2, 2009. Retrieved July 11, 2013.
^"Just Be Careful...". The Hills. Season 3. Episode 23. April 7, 2008. MTV. Archived from the original on December 31, 2013. Retrieved July 11, 2013.
^ ab"Out With The Old...". The Hills. Season 2. Episode 1. January 15, 2007. MTV. Archived from the original on August 13, 2010. Retrieved July 11, 2013.
^"With Friends Like These". The Hills. Season 2. Episode 7. February 26, 2007. MTV. Archived from the original on March 17, 2010. Retrieved July 11, 2013.
^"Forgive And Forget". The Hills. Season 3. Episode 14. November 12, 2007. MTV. Archived from the original on January 29, 2013. Retrieved July 11, 2013.
^"One Big Interruption". The Hills. Season 2. Episode 5. February 10, 2007. MTV. Archived from the original on August 13, 2010. Retrieved July 11, 2013.
^"Big Girls Don't Cry". The Hills. Season 3. Episode 2. August 14, 2007. MTV. Archived from the original on November 3, 2012. Retrieved July 11, 2013.
^"No More Mr. Nice Guy". The Hills. Season 3. Episode 11. October 22, 2007. MTV. Archived from the original on July 13, 2013. Retrieved July 11, 2013.