The 2003 FIA Formula One World Championship was the 57th season of FIA Formula One motor racing. It began on 9 March and ended on 12 October after sixteen races. World Championship titles were awarded for both drivers and constructors with Michael Schumacher winning the former and Ferrari awarded the latter.

The 2003 season saw the introduction of new regulations intended to increase F1's excitement, halt falling global TV audiences that had occurred during the previous season, and to help alleviate the financial difficulties of the smaller teams. One-lap qualifying was introduced as a way for smaller teams to get more television exposure. Optional Friday testing at Grand Prix events was introduced in exchange for fewer miles on stand-alone test days. This was intended to give smaller teams a cheaper alternative to these test days, which were to be banned in 2004. Only one type of wet weather tyre was allowed to be used in wet weather races. The points system for both the Constructors' and Drivers' titles was changed from 10–6–4–3–2–1 for the first six finishers at each round to 10–8–6–5–4–3–2–1 for the first eight finishers in an attempt to make the title contests closer.

While Ferrari's Michael Schumacher had won the 2002 championship by 67 points from his teammate Rubens Barrichello, the 2003 season was much closer. For a great part of the 2003 season, several drivers from several teams had mathematical chances of winning the world championship. Eight different drivers won a Grand Prix, amongst them three first time winners. Kimi Räikkönen, driving for McLaren-Mercedes, and Juan Pablo Montoya, driving for BMW Williams, both had a chance of claiming the 2003 championship until late in the season, with Räikkönen still mathematically in contention at the final race, the Japanese Grand Prix. Räikkönen lost the championship to Schumacher by two points, although he won only one race to Schumacher's six. It was Schumacher's sixth World Drivers' title overall, breaking Juan Manuel Fangio's 46-year-old record of five World Drivers' titles. Ferrari's defence of the Constructors' title was challenged throughout the year by Williams and McLaren, one of the few seasons where there were three front-running teams but in the end, Ferrari emerged victorious once again and the team clinched their fifth consecutive World Constructors' title since 1999.

Notable races include the chaotic Brazilian Grand Prix which was hampered by monsoon conditions and resulted in the wet weather tyre rule being reversed after just three races, and the British Grand Prix where the track was invaded by the now-defrocked priest Neil Horan, who ran onto the Hangar straight, running towards the 250 km/h train of cars, wearing a green kilt and waving religious banners.

After failing to complete the 2002 season due to financial difficulties, the Arrows team had their application for admission to the 2003 championship rejected by the FIA prior to the season start date. No reason was publicly given by the FIA and Arrows subsequently folded after 25 years in Formula One since 1978.

2003 also saw a major leap forward in Formula One safety, with the HANS device being made a mandatory requirement for drivers to wear at all races beginning from the Australian Grand Prix onwards. However, this was not without controversy, as many drivers voiced their complaints about the device, including Barrichello, Jacques Villeneuve, Justin Wilson and Nick Heidfeld.

The 2003 season is also notable for being the third and last season that fully-automatic gearboxes and launch control were allowed to be used in Formula One, since they were reintroduced in 2001. Both electronic driver aids had been used since the 2001 Spanish Grand Prix, and a rule-change in the technical regulations saw the FIA banning both systems for 2004.