The Indian Army during British rule, also referred to as the British Indian Army, was the main military force of the British Indian Empire until 1947. It was responsible for the defence of both British India and the princely states, which could also have their own armies. As quoted in the Imperial Gazetteer of India, "The British Government has undertaken to protect the dominions of the Native princes from invasion and even from rebellion within: its army is organized for the defence not merely of British India, but of all possessions under the suzerainty of the King-Emperor." The Indian Army was an important part of the forces of the British Empire, in India and abroad, particularly during the First World War and the Second World War.

The British Raj was the rule of the British Crown on the Indian subcontinent; it is also called Crown rule in India, or Direct rule in India, and lasted from 1858 to 1947. The region under British control was commonly called India in contemporaneous usage and included areas directly administered by the United Kingdom, which were collectively called British India, and areas ruled by indigenous rulers, but under British paramountcy, called the princely states. The region was sometimes called the Indian Empire, though not officially.