The McMahon Line is the boundary between Tibet and British India as agreed in the maps and notes exchanged by the respective plenipotentiaries on 2425 March 1914 at Delhi, as part of the 1914 Simla Convention.

The line delimited the respective spheres of influence of the two countries in the eastern Himalayan region along northeast India and northern Burma (Myanmar), which were earlier undefined.

The Republic of China was not a party to the McMahon Line agreement,

but the line was part of the overall boundary of Tibet defined in the Simla Convention, initialled by all three parties and later repudiated by the government of China.

The Indian part of the Line currently serves as the de facto boundary between China and India, although its legal status is disputed by the People's Republic of China. The Burmese part of the Line was renegotiated by the People's Republic of China and Myanmar.

The line is named after Henry McMahon, foreign secretary of British India and the chief British negotiator of the conference at Simla. The bilateral agreement between Tibet and Britain was signed by McMahon on behalf of the British government and Lonchen Shatra on behalf of the Tibetan government.

It spans 890 kilometres (550 miles) from the corner of Bhutan to the Isu Razi Pass on the Burma border, largely along the crest of the Himalayas.The outcomes of the Simla Conference remained ambiguous for several decades because China did not sign the overall Convention but the British were hopeful of persuading the Chinese. The Convention and the McMahon's agreement were omitted in the 1928 edition of Aitchison's Treaties. It was revived in 1935 by Olaf Caroe, then deputy foreign secretary of British India, who obtained London's permission to implement it as well as to publish a revised version of the 1928 Aitchison's Treaties.India regards its interpretation of the McMahon Line as the legal national border, but China rejects the Simla Accord and the McMahon Line, contending that Tibet was not a sovereign state and therefore did not have the power to conclude treaties. Chinese maps show some 65,000 km2 (25,000 sq mi) of the territory south of the line as part of the Tibet Autonomous Region, known as South Tibet in China. Chinese forces briefly occupied this area during the Sino-Indian War of 1962 and later withdrew. China does recognise a Line of Actual Control which closely approximates the McMahon Line in this part of its border with India, according to a 1959 diplomatic note by Prime Minister Zhou Enlai.The 14th Dalai Lama did not originally recognise India's sovereignty over Arunachal Pradesh. As late as 2003, he said that "Arunachal Pradesh was actually part of Tibet". In January 2007, however, he said that both the Tibetan government and Britain recognized the McMahon Line in 1914. In June 2008, he explicitly recognized for the first time that "Arunachal Pradesh was a part of India under the agreement signed by Tibetan and British representatives".

Ladakh () is a region administered by India as a union territory, which constitutes a part of the larger Kashmir region and has been the subject of dispute between India, Pakistan, and China since 1947. Ladakh is bordered by the Tibet Autonomous Region to the east, the Indian state of Himachal Pradesh to the south, both the Indian-administered union territory of Jammu and Kashmir and the Pakistan-administered Gilgit-Baltistan to the west, and the southwest corner of Xinjiang across the Karakoram Pass in the far north. It extends from the Siachen Glacier in the Karakoram range to the north to the main Great Himalayas to the south. The eastern end, consisting of the uninhabited Aksai Chin plains, is claimed by the Indian Government as part of Ladakh, and has been under Chinese control since 1962.In the past Ladakh gained importance from its strategic location at the crossroads of important trade routes, but as the Chinese authorities closed the borders between Tibet Autonomous Region and Ladakh in the 1960s, international trade dwindled. Since 1974, the Government of India has successfully encouraged tourism in Ladakh. As Ladakh is strategically important, the Indian military maintains a strong presence in the region.

The largest town in Ladakh is Leh, followed by Kargil, each of which headquarters a district. The Leh district contains the Indus, Shyok and Nubra river valleys. The Kargil district contains the Suru, Dras and Zanskar river valleys. The main populated regions are the river valleys, but the mountain slopes also support the pastoral Changpa nomads. The main religious groups in the region are Muslims (mainly Shia) (46%), Buddhists (mainly Tibetan Buddhists) (40%), Hindus (12%) and others (2%). Ladakh is one of the most sparsely populated regions in India. Its culture and history are closely related to that of Tibet.Ladakh was established as a union territory of India on 31 October 2019, following the passage of the Jammu and Kashmir Reorganisation Act. Prior to that, it was part of the Jammu and Kashmir state. Ladakh is the largest and the second least populous union territory of India.