Owing to its ethnic and cultural diversity, religion in Arunachal Pradesh has been a spot for the syncretism of different traditional religions. Much of the native Tani populations follow an indigenous belief which has been systematised under the banner "Donyi-Polo" (Sun-Moon) since the spread of Christianity in the region by Christian missionaries in the second half of the 20th century. The province is also home to a substantial Tibetan Buddhist population in the north and northwest who follow Tibetan Buddhism, of ethnic groups who subscribe to Hinduism, and other religious populations. Christianity is followed by over 30% of the population, mostly by natives.
Ever since the founding of the Donyi Polo religion by Daadi Botté Talom Rukbo, the indigenous religious movement has been heavily influenced by Hinduism. Donyi Poloism, along with other ancient religions,such as Hinduism, share a common belief on nature and the philosophy of maintaining the balance of nature. There was a fear among the followers in the early days of the movement that the religion would be incorporated into Hinduism as a result. This was refuted by Daadi Botté Talom Rukbo himself in a religious conference  when he established similarites between Donyi Polo and Bön, ancient Maya religion, Egyptian Ra Sun Worship, Tengri Worship & Japanese Shinto religion; and as such, all the world's ancient religions share a singular philosophy and are a part of a world community of nature worshippers and thus, asserted the need for a more independent approach. A prominent Donyi Polo worship place in Aalo town is reminiscent of a Hindu temple. External influence upon the local indigenous religious traditions has been met with increasing opposition and severity among the Tani intellectuals.
However, a large number of the Donyi Polo followers still identify themselves as Hindu in the Census because the poll does not recognise the indigenous religion and thus, avoid selecting the "others" option.
Christianity now represents about one-third of the total population. Christians, predominantly belonging to the Catholic Church, were 0.71% of the population in 1971, 10.30% in 1991 and 30.26% in 2011. According to the Swarajya magazine, the conversion of the population has been carried out through "allurements, blandishments, blatant bribery and even by force"0[better source needed]
Prior to the 1980s, Jawaharlal Nehru and his daughter Indira Gandhi affirmed that it was strategically important that Arunachal Pradesh populations were not coaxed into Christianity, so that in 1978 a law against forced conversion was passed but did not come into effect. Donyi-Poloism emerged as a self-conscious organised movement during the same years, with the aim to systematise the indigenous religions in order to prevent the takeover of Christianity.
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Migration too has been playing a major role in the changing of the religious demography of Arunachal Pradesh. The coming of Muslim populations in search of jobs and better livelihood has contributed to the growth of an Islamic community.