1991 Formula One World Championship

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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. 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.

As of 2023^[update], this is the last World Championship season to be won by a Brazilian racing driver.^[1] It was the last drivers' title won using a Honda-powered car until Max Verstappen in 2021 and the last constructors' title won by a Honda-powered car until the Red Bull Racing RB19 in 2023.

This season was the last time an F1 car with a manual gearbox won the championship, and the only V12-powered car to do so.^[2] It was also Pirelli's last season as Formula One's tyre supplier until 2011.^{[citation needed]}