The 1991 FIA Formula One World Championship was the 45th season of FIA Formula One motor racing and the 42nd season of the Formula One World Championship. It featured the 1991 Formula One World Championship for Drivers and the 1991 Formula One World Championship for Constructors, which were contested concurrently over a sixteen-race series that commenced on 10 March and ended on 3 November. Ayrton Senna won his third and last Drivers' Championship, and McLaren-Honda won their fourth consecutive Constructors' Championship.

Senna won seven of the sixteen races; his main challenger for the title was Nigel Mansell, who won five races in his first season back at Williams. Senna's fierce rival Alain Prost failed to win a race with Ferrari and was fired before the end of the season due to a dispute with the team. 1991 also saw the debuts of future world champions Michael Schumacher and Mika Häkkinen, as well as the retirement of three-time champion Nelson Piquet.

This season was the last time an F1 car won the championship with a manual gearbox and the only V12 powered car to do so. This also was Pirelli's last season as the tyre supplier for the Formula One World Championship, until they returned the sport again in 2011, where they become the sole tyre supplier for the sport in that season.