Grey's Anatomy is the hit ABC television series featuring a group of interns, residents and their menotrs at Seattle Grace Mercy West Hospital in Seattle Washington. The show premiered as a mid-season replacement for Boston Legal on March 27, 2005 and is currently in it's 6th season.

The characters of the series include a group of surgical interns, residents, and the various physicians who serve as mentors to the interns in their professional and personal lives. The first group of interns looking to make their way as surgeons were Meredith Grey (Ellen Pompeo), Alex Karev (Justin Chambers), George O'Malley (T. R. Knight), Izzie Stevens (Katherine Heigl) and Cristina Yang (Sandra Oh).  They are initially mentored by Miranda Bailey (Chandra Wilson), a general surgeon who becomes the hospital's Chief Resident and later applies for a pediatric surgery fellowship. The surgical program is run by Chief of Surgery Richard Webber (James Pickens, Jr.) who has a pre-existing personal relationship with Meredith, having had an affair with her mother when Meredith was a child. In Webber's employ are attending physicians Derek Shepherd (Patrick Dempsey) and Preston Burke (Isaiah Washington), who specialize in neurosurgery and cardiothoracic surgery respectively. Derek is introduced as Meredith's love interest, while Preston begins a relationship with Cristina.

Introduced in the show's second season are OB/GYN and neonatal surgeon Addison Montgomery (Kate Walsh), plastic surgeon Mark Sloan (Eric Dane), orthopedic surgeon Callie Torres (Sara Ramírez). Addison is Derek's wife who arrives in Seattle seeking a reconciliation with him. Mark is Derek's former best friend, who aided in the breakdown of his marriage by having an affair with Addison. Callie is introduced as a love-interest for George, who she later marries, but ultimately divorces.

Addison departed the show after the third season, as Kate Walsh left to star in spin-off Private Practice, but continues to make occasional guest appearances in Grey's Anatomy. The penultimate episode of the third season introduced intern Lexie Grey (Chyler Leigh), Meredith's half-sister. She forms a fast friendship with George. Later, in season four, the unexpected occurs and Mark Sloan embarks on a relationship with her. The finale of season three saw Preston Burke's exit from the show, after leaving Cristina at the altar.

Joining the regular cast in the fourth season was cardiothoracic surgeon Erica Hahn (Brooke Smith), a previously recurring character in seasons two and three, who began a romantic relationship with Callie. Meredith, Cristina, Izzie and Alex spend their first day as residents with their own groups of interns. Among the interns are George, repeating his intern year after failing his exams, and Lexie Grey, Meredith's half-sister whom she has never met.

During the Fifth Season, Dr. Erica Hahn is cut off the show, subsequent to her growing discontent with Callie and several other doctors at Seattle Grace. Two new characters are introduced: trauma surgeon Owen Hunt (Kevin McKidd) and pediatric surgeon Arizona Robbins (Jessica Capshaw). Owen became a love-interest for Cristina, while Arizona became a love-interest for Callie. Season five also introduced the recurring character Dr. Sadie Harris (Melissa George), who had a friendship with Meredith years before. She forms a bond with Lexie and a possible relationship with Callie. Sadie was expected to become a series regular but her contract was not renewed and her character was subsequently written out of the show.

Season Six introduced several changes: following his tragic death, the character of Dr. George O'Malley was written off the show and attending Dr. Teddy Altman (Kim Raver) joined the cast as a cardiothoracic surgeon from Owen's past. In addition, several recurring characters are introduced, in concurrence with the Mercy West and Seattle Grace hospital merger storyline. Residents Dr. Reed Adamson (Nora Zehetner), Dr. Jackson Avery (Jesse Williams) and Dr. Charles Percy (Robert Baker) all transfer to Seattle Grace hospital from Mercy West, creating friction between themselves and the Seattle Grace doctors.