A McLaren a 2006-os idényre fejlesztette ki az MP4-21-et, amelyet a leggyorsabb 2005-ös autó utódjának szántak. V8-as motor, csökkentett méretű karosszéria jellemző az autóra, melynek köszönhetően aerodinamikai tulajdonságai javultak. Az új autó 11500 alkotóelemből áll, melynek 90%-a eltér az MP4-20-tól. Ez a modell 2008-as színeket kapott.
The McLaren MP4-21 is a Formula One car designed by Adrian Newey for the 2006 Formula One season. The car continues the MP4-X naming system and is notable for its striking chrome livery which is designed to maximize the visibility of the teams sponsors.
The car started the season in the hands of Kimi Räikkönen 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. McLaren did not win a race all season, for the first time since 1996. Their best results were second place finishes for Kimi Räikkönen in Australia and Italy, for Juan Pablo Montoya in Monaco, and for Pedro de la Rosa in Hungary. After the US Grand Prix, Montoya announced that he would be leaving Formula One at the end of the season to race for Chip Ganassi's team in NASCAR; in response, McLaren agreed to release him, promoting Pedro de la Rosa into his seat for the remaining races of the season.