Christianity is the largest religion in Tanzania according to the most recent estimates. Current statistics on the relative sizes of various religions in Tanzania are limited because religious questions have been eliminated from government census reports since 1967. A 2014 survey from the Pew Research Center found that 61% of the population are Christian, 35% are Muslim, 2% practice traditional religions and 1% are unaffiliated.
For many years estimates have been repeated that about a third of the population each follows Islam, Christianity and traditional religions.
Religion-related statistics for Tanzania have been regarded as notoriously biased and unreliable.
About 98 percent of the population in Zanzibar is Muslim. There are also active communities of other religious groups, primarily on the mainland, such as Buddhists, Hindus, Sikhs, and Bahá'ís. A 2015 study estimates some 180,000 Christian believers from a Muslim background in the country, most of whom are Protestants of some form.
The Christian population is largely composed of Roman Catholics and Protestants. Among the latter, the large number of Lutherans and Moravians point to the German past of the country while the number of Anglicans point to the British history of Tanganyika. All of them have had some influence in varying degrees from the Walokole movement (East African Revival), which has also been fertile ground for the spread of charismatic and Pentecostal groups.
On the mainland, Muslim communities are concentrated in coastal areas, with some large Muslim majorities also in inland urban areas especially and along the former caravan routes. The majority of the country's Muslim population is Sunni of Shafi school of jurisprudence; the remainder consists of several Shia subgroups (20%), mostly of Asian descent and the Ahmadiyya Islamic movement (15%).
The Constitution provides for freedom of religion, and the Government generally respects this right in practice. There have been cases of increased tension between moderate and fundamentalist Muslims as the latter have called for Muslims to adopt a stricter interpretation of Islam in their daily lives.