The 2005 FIA Formula One World Championship was the 59th season of FIA Formula One motor racing. It featured the 56th FIA Formula One World Championship, contested over a then-record 19 Grands Prix. It commenced on 6 March and ended 16 October.

Fernando Alonso and the Renault team won the World Drivers' and World Constructors' championships, ending five years of dominance by Michael Schumacher and Ferrari since 2000 and also ending nine years of Ferrari, McLaren and Williams dominance triopoly since 1996. Alonso's success made him the youngest champion in the history of the sport, a title he held until Lewis Hamilton's 2008 title success. Renault's win was their first as a constructor. Alonso started the season off strongly, winning three of the first four races and his title success was in little doubt. He sealed the title in Brazil with two races left after a controlled third-place finish. Alonso's championship was also the first for a Renault-powered driver since Jacques Villeneuve's championship in 1997.

Alonso and Renault had to contend with the pace of the resurgent McLaren team with lead driver Kimi Räikkönen outshining teammate Juan Pablo Montoya, who came highly regarded from his time at Williams. Räikkönen won seven races like Alonso but would have won more if not for a series of reliability issues, resulting in qualifying engine change penalties and retirements from the lead on three occasions. Nevertheless, Räikkönen grabbed the headlines winning from near the back of the grid in Japan, passing Alonso's Renault teammate Giancarlo Fisichella on the final lap. Reigning champions Michael Schumacher and Ferrari had a poor season by their standards, with Bridgestone unable to compete with Michelin after the tyre-change ban that only affected the 2005 season. Their only win came when Michelin deemed their own tyres unsafe after several incidents in the oval turn at Indianapolis. As a result, only the six Bridgestone cars took part. Schumacher just held on for third in the Drivers' Championship, in spite of the superior pace of McLaren, underlining the disappointing season Montoya had. The Colombian missed two races early on due to a tennis injury. He then won three races, showing glimpses of pace, but was well beaten by his teammate Räikkönen in the championship.

The 2005 season was the last before the Minardi, BAR and Jordan teams were taken over by new owners and changed names to Toro Rosso, Honda, and Midland respectively in the 2006 season. The former Jaguar team was sold from Ford to Red Bull GmbH and made its debut as Red Bull Racing during the 2005 season.