The third season of the American television medical drama Grey's Anatomy, commenced airing on the American Broadcasting Company (ABC) on September 21, 2006, and concluded on May 17, 2007. The season was produced by Touchstone Television, in association with Shondaland Production Company and The Mark Gordon Company, the showrunner being Shonda Rhimes. Actors Ellen Pompeo, Sandra Oh, Katherine Heigl, Justin Chambers and T. R. Knight reprised their roles as surgical interns Meredith Grey, Cristina Yang, Izzie Stevens, Alex Karev and George O'Malley, respectively, continuing their expansive storylines as focal points throughout the season. Previous main cast members Chandra Wilson, James Pickens, Jr., Kate Walsh, Isaiah Washington, and Patrick Dempsey also returned, while previous guest-stars Sara Ramirez and Eric Dane were promoted to series-regulars, following the extension of their contracts.

Grey's Anatomy is an American medical drama television series focusing on the personal and professional lives of surgical interns, residents, and attendings at the fictional Seattle Grace Hospital, later named the Grey Sloan Memorial Hospital. The series premiered on March 27, 2005, on ABC as a mid-season replacement. The show's title is an allusion to Gray's Anatomy, a classic human anatomy textbook. Writer Shonda Rhimes developed the pilot and served as showrunner, head writer, and executive producer until stepping down in 2015. Set in Seattle, Washington, the series is filmed primarily in Los Angeles, California, and Vancouver, British Columbia.