Fifteen to One was a popular general knowledge quiz show broadcast on Channel 4 in the United Kingdom. It ran from 4 January 1988 to 19 December 2003, and had a reputation for being one of the toughest quizzes on TV. Throughout the show's run it was presented and produced by William G. Stewart. Some 30,000 contestants appeared on the programme, which was notable for having very little of the chatting between host and contestant that is often a feature of other television quiz shows.

The basis of the show was devised by John M. Lewis, a former sales manager for British Telecom. He submitted the idea to Regent Productions who developed the programme into a 30 minute format. Originally, there were 20 starting contestants but the figure was cut down to 15 in order to fit the available running time. The number varied in other countries.

The Fifteen to One format is sold internationally by DRG-Zeal TV from London.

At the start of the grand finale of the 35th and final series, William G. Stewart provided some statistics about the show, stating that nearly 350,000 questions had been asked to 33,975 contestants in a total of 2265 programmes.

On 20 September 2013, a special one-off episode aired on Channel 4. The show was hosted by Adam Hills and titled Celebrity Fifteen to One.