Si-Donyi is the major festival celebrated among the Tagin tribe of Arunachal Pradesh in North-eastern India. It is celebrated majorly in district headquarter Daporijo, in adjoining town Dumporijo and in Taliha, Siyum areas, also in state capital Itanagar, while in other places also it's being celebrated by Tagin community present there.The festival was first conceptualised in the year 1975 by lt.Tatar Uli, who was the main pioneer in inception of Si-Donyi. The other members who bore the responsibilities were lt.Tadak Dulom and Popak Baghe. The festival was celebrated in the same year under their guidance, and since then, the festival Si donyi has been celebrated by the Tagin tribe.The first priest who led the ritual was Dubi Nigam. Further the name SiDonyi was suggested by Shri. Bingsa Kod