The Sino-Indian War ( ; Hindi: भारत-चीन युद्ध Bhārat-Chīn Yuddh), also known as the Sino-Indian Border Conflict, was a war between People's Republic of China and India. The initial cause of the conflict was a disputed region of the Himalayan border in Arunachal Pradesh, known in China as South Tibet. Fighting began on 20 October 1962 between the People's Liberation Army and the Military of India. The first heavy engagement of the war was a Chinese attack on an Indian patrol north of the McMahon Line. The conflict eventually widened to include the region of Aksai Chin which the PRC regarded as a strategic link, via the China National Highway route G219, between the Chinese-administered territories of Tibet and Xinjiang. The war ended when the Chinese captured both disputed areas and unilaterally declared a ceasefire on 20 November 1962, which went into effect at midnight.

The Sino-Indian War is notable for the harsh conditions under which much of the fighting took place, entailling large-scale combat at altitudes of over 4250 metres (14,000 feet). This presented numerous logistical problems for both sides.

The aftermath of the war saw sweeping changes in the Indian military to prepare it for similar conflicts in the future, and placed pressure on Indian prime minister Jawaharlal Nehru, who was seen as responsible for failing to anticipate the Chinese invasion.