Crimewatch (formerly Crimewatch UK) is a British television programme produced by the BBC, that reconstructs major unsolved crimes in order to gain information from the public which may assist in solving the case. The programme was originally broadcast once a month in a primetime slot on BBC One, although in the final years before its relaunch in September 2016 it was usually broadcast roughly once every two months.

Crimewatch was first broadcast on 7 June 1984, and is based on the German TV show Aktenzeichen XY… ungelöst (which translates as File Reference XY … Unsolved). Nick Ross and Sue Cook presented the show for the first eleven years, until Cook's departure in June 1995. Cook was replaced by Jill Dando. After Dando was murdered in April 1999, Ross hosted Crimewatch alone until January 2000, when Fiona Bruce joined the show.

Kirsty Young and Matthew Amroliwala replaced Ross and Bruce following their departures in 2007. The BBC announced on 15 October 2008 that they would move production of shows such as Crimewatch to studios in Cardiff. The move took place in January 2011. Young and Amroliwala remained as the lead presenters until 2015. Following a brief period with guest presenter Sophie Raworth in 2016, it was announced that the show would relaunch in September 2016 with a new weekly format. The new presenters were announced as Jeremy Vine and Tina Daheley. The new series began on 5 September 2016, with the final episode broadcast on 20 March 2017.

In October 2017, the BBC announced that the main Crimewatch series had been cancelled, citing declining viewership. The daytime spin-off series Crimewatch Roadshow (now Crimewatch Live) would continue to air, but will also air more episodes per year. Over 40 years, more than 700 programmes have been broadcast with 7,000 appeals made on behalf of British police.

The idea for the show came from the UK programme Police 5 and the German Aktenzeichen XY… ungelöst (File Reference XY … Unsolved). Producers viewed the shows and rejected the overt reconstructions with music to build suspense in America's Most Wanted, and were also against the idea of filming the reconstruction from the perspective of the offender as in Aktenzeichen XY… ungelöst (particularly for sexual assaults). However, they favoured the idea of audience participation in the show.

Originally, Crimewatch UK (as it was then known) was due to run for only three programmes. It was regarded as an experiment when it was first shown due to doubts that the police would take part and scepticism as to whether witnesses and victims would welcome the idea. There was also concern that it could be considered to prejudice a jury. In over 25 years, 57 murderers, 53 rapists and sex offenders, 18 paedophiles, and others were captured as a direct result of Crimewatch appeals.

The original theme music was "Rescue Helicopter" (1980) by John Cameron (Bruton Music).

Crimewatch used to be shown once a month on BBC One. The start time varied slightly but it was generally aired for 45–50 minutes before being extended to an hour in the early 2000s. In the early years it followed the BBC Nine O'Clock News starting at around 9.30pm but in the mid to late 1990s was often moved to 10pm, always with a short Crimewatch Update programme airing later that evening (sometimes as late as after midnight due to scheduling). In June 1986 there was no edition of the programme due to World Cup football coverage from Mexico. In January 1987 the Grandstand studio was used for that month's edition due to a strike by the set designers. In later years, following the move of the flagship evening news programme, the main show was now aired at 9pm for an hour with Crimewatch Update now airing sometime after the BBC Ten O'Clock News. Since March 2011 the show aired less frequently, roughly once every two months.