The 1991 FIA Formula One World Championship was the 45th season of FIA Formula One motor racing. It featured the 1991 FIA Formula One World Championship, which commenced on 10 March 1991 and ended on 3 November after sixteen races. Ayrton Senna won his third and last Drivers' World 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 world champion Nelson Piquet.