The attack on Pearl Harbor was a surprise attack against the United States' naval base at Pearl Harbor, Hawaii by the Japanese navy, on the morning of Sunday, December 7, 1941, resulting in the United States becoming involved in World War II. It was intended as a preventive action to remove the US Pacific Fleet as a factor in the war Japan was about to wage against Britain, the Netherlands, and the United States. Two aerial attack waves, totaling 353 aircraft, launched from six Japanese aircraft carriers, intending to reduce or eliminate United States' military power in the Pacific.

The attack wrecked two U.S. Navy battleships, one minelayer, and two destroyers beyond repair, and destroyed 188 aircraft; personnel losses were 2,388 killed and 1,178 wounded. Damaged warships included three cruisers, a destroyer, and six battleships (one deliberately grounded, later refloated and repaired; two sunk at their berths, later raised, repaired, and eventually restored to Fleet service). Vital fuel storage, shipyard, maintenance, and headquarters facilities were not hit. Japanese losses were minimal, at 29 aircraft and five midget submarines, with 65 servicemen killed or wounded.

The intent of the strike was to protect Imperial Japan's advance into Malaya and the Dutch East Indies — for their natural resources such as oil and rubber — by neutralizing the U.S. Pacific Fleet. Both the U.S. and Japan had long-standing contingency plans for war in the Pacific, continuously updated as tension between the two countries steadily increased during the 1930s. Japan's expansion into Manchuria and French Indochina were greeted with steadily increasing levels of embargoes and sanctions by the United States and others. In 1940, under the Export Control Act, the U.S. halted shipments of airplanes, parts, machine tools, and aviation gasoline, which Japan saw as an unfriendly act. After it was announced in September export of iron and steel scrap would be prohibited, Japanese Ambassador Horinouchi protested to Secretary Hull on October 8, 1940, this might be considered an "unfriendly act". Nevertheless, the U.S. continued to export oil to Japan, in part because it was understood in Washington cutting off oil exports would be an extreme step, given Japanese dependence on U.S. oil exports, . likely to be taken as a provocation by Japan. In the summer of 1941, after Japanese expansion into French Indochina, the U.S. ceased oil exports to Japan, in part because of new American restrictions on domestic oil consumption. . President Franklin D. Roosevelt had earlier moved the Pacific Fleet to Hawaii and ordered a buildup in the Philippines, hoping to deter Japanese aggression in the Far East. The Japanese high command was (mistakenly) . certain an attack on the United Kingdom's colonies would bring the U.S. into the war, . so a preventive strike appeared to be the only way Japan could avoid U.S. interference in the Pacific. While it accomplished the intended objective, unbeknownst to Isoroku Yamamoto, who planned the attack and commanded the attacking force, the attack was pointless. The U.S. Navy in 1935 had abandoned any intention of attempting to charge across the Pacific towards the Philippines at the outset of war (in keeping with the evolution of War Plan Orange), and in 1940 adopted "Plan Dog", which emphasized keeping the Imperial Japanese Navy (IJN) out of the eastern Pacific and away from the shipping lanes to Australia, while the U.S. concentrated on defeating Nazi Germany.

The attack was one of the most important engagements of World War II. Occurring as it did before a formal declaration of war, it pushed U.S. public opinion from isolationism to an acceptance war was unavoidable, as Roosevelt called December 7, 1941 "... a date which will live in infamy."