The British expedition to Tibet, also known as the Younghusband expedition, began in December 1903 and lasted until September 1904. The expedition was effectively a temporary invasion by British Indian Armed Forces under the auspices of the Tibet Frontier Commission, whose purported mission was to establish diplomatic relations and resolve the dispute over the border between Tibet and Sikkim. In the nineteenth century, the British had conquered Burma and Sikkim, with the whole southern flank of Tibet coming under the control of the British Indian Empire. Tibet ruled by the Dalai Lama under the Ganden Phodrang government was a Himalayan state under the protectorate (or suzerainty) of the Chinese Qing dynasty until the 1911 Revolution, after which a period of de facto Tibetan independence (1912–1951) followed.

The invasion was intended to counter the Russian Empire's perceived ambitions in the East and was initiated largely by Lord Curzon, the head of the British Indian government. Curzon had long held deep concerns over Russia's advances in central Asia and now feared a Russian invasion of British India. In April 1903, the British government received clear assurances from Russia that it had no interest in Tibet. "In spite, however, of the Russian assurances, Lord Curzon continued to press for the dispatch of a mission to Tibet", a high level British political officer noted.

The expeditionary force fought its way to Gyantse and eventually reached Lhasa, the capital of Tibet, in August 1904. The Dalai Lama had fled to safety, first to Mongolia and then to China proper. The poorly-trained and equipped Tibetans proved no match for the modern equipment and training of the British Indian forces. At Lhasa, the Commission forced remaining Tibetan officials to sign the Convention of Lhasa, before withdrawing to Sikkim in September, with the understanding the Chinese government would not permit any other country to interfere with the administration of Tibet.