The Williams FW09 was a Formula One car designed by Frank Dernie and Neil Oatley. It was the first Williams chassis to be powered by a turbocharged Honda V6 engine, for which Frank Williams negotiated a deal towards the end of 1982 and the beginning of 1983.

Honda was already supplying the small Spirit team for 1983, but was enthusiastic about supplying Williams, who not only had the reigning World Champion Keke Rosberg as lead driver, but were one of the leading constructors in Formula One who had previously won both the Drivers' and Constructors titles on two occasions, a résumé that neither Spirit nor their young Swedish driver Stefan Johansson could match. Williams had agreed to help develop the engine under Grand Prix race conditions. Spirit folded shortly afterwards.