WilliamsF1, the trading name of Williams Grand Prix Engineering Ltd., is a Formula One (F1) motor racing team and constructor. It was founded and run by Sir Frank Williams and Patrick Head. The team was formed in 1977 after two earlier and, compared with WilliamsF1's achievements, unsuccessful F1 operations, Frank Williams Racing Cars and Walter Wolf Racing. All of WilliamsF1 chassis are called "FW" then a number, the FW being the initials of team owner, Frank Williams.

Williams' first race was the 1977 Spanish Grand Prix, where the new team ran a March chassis for Patrick Nève. Williams started manufacturing its own cars the following year, and Switzerland's Clay Regazzoni won Williams' first race at the 1979 British Grand Prix. At the 1997 British Grand Prix, Canadian Jacques Villeneuve won the team's 100th race, making Williams one of only three teams in Formula One, alongside Ferrari and fellow British team McLaren, to win 100 races. Williams won nine Constructor's titles between 1980 and 1997. This stood as a record until Ferrari surpassed it in 2000.

Many famous racing drivers have driven for Williams, including Australia's Alan Jones; Finland's Keke Rosberg; Britain's Nigel Mansell and Damon Hill; France's Alain Prost; Brazil's Nelson Piquet and Ayrton Senna, and Canada's Jacques Villeneuve, each of whom, with the exception of Senna, have captured one Drivers' title with the team. After Senna died in a Williams car in a crash at the 1994 San Marino Grand Prix, Frank Williams, Patrick Head and designer Adrian Newey were all accused of manslaughter. The trial finally closed in 2005, when Williams, Head and Newey were cleared of any wrongdoing.

Williams have worked with many notable engine manufacturers, most successfully with Renault: Williams won five of their nine constructors' titles with the French company. Along with Ferrari, McLaren, and Renault (formerly Benetton), Williams is one of the "Big Four" teams that have won every constructors' championship since 1979 and every driver's championship since 1984. Williams remains the only one independently owned, as the other three "factory teams" have been set up by or bought out by major automobile manufacturers.

Frank Williams started the current Williams team in 1977 after his previous outfit, Frank Williams Racing Cars, failed to achieve the success he desired. Despite the promise of a new owner in the form of Canadian millionaire Walter Wolf, the team's 1976 cars were not competitive. Eventually Williams left the rechristened Walter Wolf Racing and moved to Didcot to rebuild his team as "Williams Grand Prix Engineering". Frank recruited young engineer Patrick Head to work for the team, creating the "Williams-Head" partnership.