The 1991 United States Grand Prix was a Formula One motor race held on March 10, 1991 in Phoenix, Arizona. It was the first race of the 1991 Formula One World Championship. The race was won from pole position by Ayrton Senna, driving a McLaren-Honda, with Alain Prost second in a Ferrari and Nelson Piquet third in a Benetton-Ford.

The race marked the respective debuts of future double World Champion Mika Häkkinen and the Jordan team. It was also the first F1 World Championship race in which ten points were awarded for a win rather than nine, as part of a revised scoring system introduced for 1991.