The Imperial Japanese Army (IJA) was the official ground based armed force of Imperial Japan from 1867 to 1945. It was controlled by the Imperial Army General Staff Office and the Ministry of War, both of which were nominally subordinate to the emperor as supreme commander of the army and the navy. Later an Inspectorate General of Military (Army) Aviation, became the third agency with oversight over the army. During wartime or national emergencies, the nominal command functions of the emperor would be centralized in an Imperial General Headquarters (IGHQ), an ad-hoc body consisting of the chief and vice chief of the Army General Staff, the minister of war, the chief and vice chief of the Naval General Staff, the inspector general of military aviation, and the inspector general of military training.

In 1941, the Imperial Japanese Army had 51 divisions and various special-purpose artillery, cavalry, anti-aircraft and armored units with a total of 1,700,000 men. At the beginning of the Second World War most of the Japanese Army was stationed in China. However, from 1942 soldiers were sent to Hong Kong (23rd Army), the Philippines (14th Army), Thailand (15th Army), Burma (15th Army), Dutch East Indies (16th Army) and Malaya (25th Army). The Japanese Army performed well in the early stages of the war. After 1943 they suffered from a shortage of supplies, to include heavy weapons, guns, tanks and aircraft, and was worsened by a long-standing and severe rivalry with the Imperial Japanese Navy. By 1945 there were 5.5 million men in the Imperial Japanese Army.

Throughout the Second Sino-Japanese War and World War II, the Imperial Japanese Army had gained a reputation both for its fanaticism and for its brutality against prisoners of war and civilians alike. After Japan surrendered in the summer of 1945, many Imperial Japanese Army officers and enlisted men were tried and punished for committing numerous atrocities and war crimes. Several reasons are theorized for the especially brutal and merciless behavior exhibited by many members of the IJA towards their adversaries or non-Japanese civilians. One is probably the brutal behavior that they themselves experienced. The IJA was known for the extremely harsh treatment of its enlisted soldiers, including beatings, unnecessarily strenuous duty tasks, lack of adequate food, and other violent or harsh disciplinary tactics. After the defeat of Japan in World War II, the Imperial Japanese Army was formally dissolved in September 1945 by the U.S. occupying forces.

In 1947 the Japanese formed the Public Security Force which later in 1954, formed the basis of the newly created Ground Self Defense Force. These forces, though significantly smaller than the Imperial Japanese Army and purely for defense, constitute the modern army of Japan.