No. 303 Squadron RAF, also known as the 303rd "Tadeusz Kościuszko Warsaw" Fighter Squadron, was one of two Polish squadrons that fought during the Battle of Britain, and one of sixteen Polish squadrons that served in the RAF during World War II. Flying Hawker Hurricanes, the squadron was ranked first among all 66 Allied fighter squadrons engaged in the Battle of Britain with 75 verified victories — despite joining the battle two months after it had begun.

The squadron was formed in July 1940 in Blackpool, England, under the agreement between the Polish Government in Exile and the United Kingdom. It was equipped with Hawker Hurricanes and deployed to RAF Biggin Hill in August 1940 as part of No. 10 Group, Fighter Command. Among its pilots was Flying Officer Josef František, a Czech pilot who served with the squadron and became one of the highest-scoring pilots of the battle with 17 confirmed victories, all achieved in just 10 days of combat.

The squadron proved that Polish pilots, with their extensive combat experience from the invasion of Poland and the fall of France, were amongst the most skilled fighter pilots in the RAF. Their performance at Biggin Hill during the Battle of Britain remains one of the most remarkable stories of aerial warfare. The squadron was disbanded in December 1946.