The Ao are a Naga people of Nagaland in north-east India. Their main territory is from Tsula (Dikhu) Valley (in the east) to Tsurang (Disai) Valley (in the west) in Mokokchung District. They are well known for multiple harvest festivals held each year.
According to the 2010 census of India, Ao Nagas number 231,823.
Ao Nagas are found in the north-eastern part of Nagaland, mostly in the central Mokokchung District and also few are found in the adjacent Assam state. Mokokchung, one of the districts in Nagaland, is considered as the home of the Ao Naga tribe. It covers an area of 1,615 km2 and is bounded by Assam to its north, Wokha to its west, Tuensang to its east, and Zunheboto to its south. The physiography of the district shows six distinct hill ranges which are more or less parallel to each other and run in the south-east direction.
Tzurangkong Range: These are actually pimples of hillocks thrown at random. They lay adjoining the plains of Assam mostly along the valley of Dissai and Jhanzi rivers just before they flow into the plains of Assam. These hillocks are densely covered with bamboos and the climate of the entire range is warm.
Japukong Range: It is the outermost range stretching from north-east to south-west lying to the interior south of Tzurangkong Range.
Changkikong Range: This is a parallel range east of the Japukong Range. The Changki village was said to be founded by a man named Changki, and so the range too was named after him as Changkikong.
Asetkong Range: It is a central range running from east to west but compared to the other ranges, it is the shortest one. This range lies between Melak and Menung rivers, and therefore, it resembles an island. Hence the name Asetkong (Aset meaning Island)
Langpangkong Range: It is the eastern-most range skirting along the course of Dikhu River. The river forms a natural boundary line of Mokokchung with Tuensang and Mon districts. This range is spread like a bed and so the name has been aptly given to this range. (Langpang means bed)
Onpangkong Range: It is the southern-most range forming an irregular boundary of the Ao area with that of the Lothas and Semas to the south and with the Sangtams to the east. It is called Ongpangkong as the land is higher and cooler than the other ranges. (Ongpang means higher)
Two informative documentaries by Moasunep Kichu offer several other interesting details about this tribe and their history. Part one deals with their origin and migration. Video link  The other one reflects on their dress, ornaments, tattoos, food habits and language. Video link 
With the arrival of Christian missionaries in the 19th century the Ao were some of the earliest converts to Christianity among the other Naga tribes. Many became Christians in the 1870s. Today, Aos are almost 100 percent Christians, the majority being Baptists. Many Ao people have undertaken missionary work in other areas as well.
- Mills, J. P. (1926). The Ao Nagas. London: Macmillan and Co.
- Smith, William C. (2002). The Ao-Naga tribe of Assam. New Delhi: Mittal.
- Oppitz, Michael, Thomas Kaiser, Alban von Stockhausen & Marion Wettstein. 2008. Naga Identities: Changing Local Cultures in the Northeast of India. Gent: Snoeck Publishers.
- Kunz, Richard & Vibha Joshi. 2008. Naga – A Forgotten Mountain Region Rediscovered. Basel: Merian.
- Alban von Stockhausen: Imag(in)ing the Nagas: The Pictorial Ethnography of Hans-Eberhard Kauffmann and Christoph von Fürer-Haimendorf. Arnoldsche, Stuttgart 2014, ISBN 978-3-89790-412-5.
- Census of Government of India, 2001