Sir Henry McMahon, a British colonial administrator, drew a line along the Himalayas at the Simla Convention of 1913-14, demarcating what would in later years become the effective boundary between China and India. The boundary, disputed by India's northern neighbour, has had a profound effect on the relations between the two Asian giants, resulting most prominently in the war of 1962 but also in several skirmishes and stand-offs both before and after that. It continues to be a thorn in the side - reaching a flashpoint at the tri-junction between Tibet, Sikkim and Bhutan in Doklam in 2017 - and may derail all the progress in bilateral ties if left unattended. General J.J. Singh examines the evolution of the boundary and the nuances of British India's Tibet policy from the eighteenth century through to India's Independence, analyses the repercussions for contemporary times and puts forth recommendations for the way ahead.