The Williams FW11 is a Formula One car designed by Frank Dernie for the Williams team. The original FW11 was used in the 1986 Formula One World Championship while an updated version, the FW11B, was used in the 1987 Championship. In both years, the car was powered by a Honda 1.5-litre turbocharged V6 engine, and driven by Briton Nigel Mansell and Brazilian Nelson Piquet.

The original FW11 won nine races of the 1986 Championship, with both Mansell and Piquet challenging for the Drivers' title before dramatically losing out to Alain Prost in his McLaren in the final race of the season in Australia. The FW11B won nine races of the 1987 Championship, and Piquet won the Drivers' title despite winning fewer races than Mansell. In both years, Williams comfortably won the Constructors' title.

The FW11B was the last Williams car with a turbocharged engine until the FW36 in 2014.