The North East Frontier Agency, formerly known as the North East Frontier Tracts, was one of the political units of the British Empire in India which supervised and managed a number of princely states of India. It was formed entirely of princely states of India that were governed by native rulers and Indian princes. The agency was managed by a resident of British India, also known as political agent, who officially served as a diplomat but was also responsible for keeping the ruler to maintain the association and alliance with the British administration. The British Resident was a government official who took up residence in a princely state and conducted several official diplomatic functions that aided in the British indirect rule. After Indian Independence, the North East Frontier Agency became a Political office of the Republic of India until 1972, when it was made a part of the Union Territory of Arunachal Pradesh. Till the year 1974, the administrative headquarters of the territory was at Shillong, after which it was reassigned to Itanagar.

History of North East Frontier Agency
In the year 1914, some of the regions, which were primarily tribal, were segregated from the former districts of Darrang and Lakhimpur of Assam Province in British India in order to create the North East Frontier Tracts (NEFT). It was originally divided into 2 segments, the Central Section and the Eastern Section, which comprised the previous Dibrugarh Frontier Tract, formed in 1882, and some other regions in south; and the Western Section. Each of the sections was under the management of a political officer, also known as resident of British India. The Central and Eastern Section was renamed as Sadiya Frontier Tract and the Western Section was renamed as Balipara Frontier Tract in the year 1919. Later in 1937, Balipara and Sadiya Frontier Tracts, including the Lakhimpur Frontier Tract, which was also formed in 1919, of Assam Province was jointly known as the Excluded Areas of province of Assam under the provisions of Government of India Act, 1935.

Tirap Frontier Tract was formed through the Regulation 1 of 1943 (The North Eastern Frontier Tracts- Internal Administration Regulation 1943) by merging certain regions of Lakhimpur and Sadiya Frontier Tracts. In the year 1946, Balipara Frontier Tract was split into 2 administrative units, namely Subansiri Area and Sela Sub-Agency. After the nation achieved independence from the British Government of India in 1947, the North East Frontier Tracts became a part of the state of Assam. Later, Sadiya Frontier Tract was divided into 2 districts in 1948, Mishmi Hills district and the Abor Hills district. The plain areas of these tracts, namely Mishimi Hills district, Abor Hills district, Tirap Frontier Tract and Balipara Frontier Tract, were reassigned to the Assam state government. The rest of the region became one of the Tribal Areas in Assam state (under part-B of the table appended to paragraph 20 of the sixth schedule of the Indian constitution). The Mishmi Hills district, Abor Hills district, Tirap Frontier Tract, Balipara Frontier Tract and the Naga tribal areas were collectively named as the North East Frontier Agency (NEFA) in the year 1951.

The North East Frontier Agency was separated into 6 frontier divisions, namely Tuensang, Lohit (previously Mishmi Hills district), Siang (previously Abor Hills district), Tirap (previously Tirap Frontier Tract), Subansiri (formerly Subansiri area) and Kameng (previously Sela Sub-Agency) on 26th January 1954. Later Tuensang was divided and merged with the newly created Naga Hills district on 1st December 1957. This was done to create the Naga Hills Tuensang Area. On 1st August 1965, the administration of the North East Frontier Agency was reassigned to the Ministry of Home Affairs from the Ministry of External Affairs. Accordingly, the 5 frontier divisions of Tirap, Lohit, Siang, Subansiri and Kameng became the 5 districts. A deputy commissioner became the administrative head of the 5 districts instead of a political officer.

An Agency Council was constituted in the year 1967 for enhanced administration. The agency was constitutionally a part of Assam state until 1972 and was administered directly by the President of India and the governor of Assam served as its agent. The North-East Frontier Agency became the Union Territory of Arunachal Pradesh on 21st January 1972 and was placed under the management of a Chief Commissioner.