The McLaren MP4-21 is a F1 car built for the 2006 F1 season. The chassis was designed by Adrian Newey, Paddy Lowe, Tim Goss, Mike Coughlan and Peter Prodromou with Mario Illen designing the bespoke Mercedes-Benz engine. The car continues the MP4-X naming system and is notable for its striking chrome livery with red stripes designed to maximize the visibility of the team's new primary sponsor Emirates. The distinctive needle-nose design was previously used on the MP4/19 in 2004. The MP4-21 was the first Mclaren car to be powered by purely Mercedes-Benz engines after 11 years partnership with Ilmor as an engine builder.

The car started the season in the hands of Kimi Raikkonen and Juan Pablo Montoya, but after a few races it soon became clear that it was not as competitive as its predecessor, the MP4/20, with an apparent improvement in reliability countered by an underpowered Mercedes engine. Mclaren did not win a race all season, for the first time since 1996. Their best results were second-place finishes for Kimi Raikkonen in Australia and Italy, for Juan Pablo Montoya in Monaco, and for Pedro de la Rosa in Hungary.

McLaren used 'Johnnie Walker' logos, except at the French and Turkish Grands Prix. In Turkey, Johnnie Walker was replaced with the Diageo logo.