Holby City (stylised on-screen as HOLBY CI+Y) is a British medical drama television series that aired weekly on BBC One. It was created by Tony McHale and Mal Young as a spin-off from the established BBC medical drama Casualty, and premiered on 12 January 1999; the show ran until 29 March 2022. It follows the lives of medical and ancillary staff at the fictional Holby City Hospital, the same hospital as Casualty, in the fictional city of Holby, and features occasional crossovers of characters and plots with both Casualty (which include dedicated episodes broadcast as Casualty@Holby City) and the show's 2007 police procedural spin-off HolbyBlue. It began with eleven main characters in its first series, all of whom subsequently left the show. New main characters were then periodically written in and out, with a core of around fifteen main actors employed at any given time. In casting the first series, Young sought actors who were already well known in the television industry, something which has continued throughout its history, with cast members including Patsy Kensit, Jane Asher, Robert Powell, Ade Edmondson and John Michie.

McHale was the show's lead writer for several years, and was the first British writer ever to become the showrunner of a major prime-time drama. Under his tenure as executive producer, attempts were made at modernising the programme and appealing to a younger audience by taking on the filmizing technique and introducing musical montage segments into each episode. Twenty-three series of Holby City aired, with the final series concluding on 29 March 2022. The show ran for over 1000 hour-long episodes. It was filmed at the BBC Elstree Centre in Hertfordshire, and has featured special episodes filmed on location abroad. From October 2010, Holby City moved to high definition broadcasting. Its first executive producers were Young and Johnathan Young, who were succeeded by Kathleen Hutchison from 2002 to 2004, Richard Stokes from 2004 to 2006, McHale from 2006 to 2010, Belinda Campbell from 2010 to 2011, Johnathan Young from 2011 to 2013, Oliver Kent from 2013 to 2017 and Simon Harper from 2017 to 2021. Holby City aired once a week, all year round, and each series contained 52 episodes.

Holby City has attracted comparisons to other medical dramas, often unfavourable, and figures within the television and entertainment industry, including Broadcasting Standards Commission director Paul Bolt, have accused the BBC of squandering the television licence fee on the programme. The series employs a team of researchers to ensure medical accuracy, and utilises surgeons from different disciplines to check scripts. Cast members are taught to perform basic medical procedures, and given the opportunity to spend time on real hospital wards for research. Holby City has, however, been criticised for its lack of realism, with the British Medical Association denouncing its portrayal of organ donation and unrealistic impression of resuscitation, and an accident and emergency nurse at the 2008 Royal College of Nursing conference accusing the show of fostering unrealistic expectations of the NHS and fuelling compensation culture.

Holby City has been nominated for over 100 television awards, of which it has won ten: the 2008 British Academy Television Award for Best Continuing Drama, one BEFFTA Award, two Ethnic Multicultural Media Awards, two Music Video and Screen Awards, and four Screen Nation Awards. The show's first series averaged 9.27 million viewers, but apart from a rise in its fifth series, ratings declined year-on-year until 2009, with the eleventh series averaging 5.44 million viewers. The twelfth series saw a small rise to 5.62 million. Later series consistently drew over 4 million viewers per week.