According to 2010 government statistics, Christian groups form about 96% of the Kiribati population by census counts, most of whom are either Catholic or members of the Kiribati Uniting Church. Persons with no religious affiliation account for about 0.05% of the population. Members of the Catholic Church are concentrated in the northern islands, while Protestants are the majority in the southern islands.
Missionaries introduced Christianity into the area in the mid-19th century. The Rev. Samuel James Whitmee, of the London Missionary Society, visited the islands in 1870. Missionaries continue to be present and operate freely. The Constitution provides for freedom of religion, and the government generally respects this right. Societal abuses or discrimination based on religious belief or practice occur, but are relatively infrequent.
Catholicism is the single largest religion in Kiribati with over 50% of the population. Catholic missionaries were amongst the first Europeans to settle in Kiribati and in 1897 the first permanent structures were in place when it became part of the Apostolic vicariate of Gilbert Islands. In 1966 it was raised to the status of diocese and became known as the Diocese of Tarawa. In 1978, the year before independence, it changed names and became known as the Diocese of Tarawa, Nauru and Funafuti. Nauru and Funafuti were part of the Apostolic Vicariate. Four years later Funafuti split and became a Mission Sui Iuris. The remaining structure today is the Diocese of Tarawa and Nauru and is led by Bishop Koru Tito, and emeritus Paul Mea.
The Church of Jesus Christ of Latter-Day Saints claims 17,462 members in 26 congregations on December 31, 2016, though the 2015 census had only 5,857 people (5.3%) identifying as Mormon. From church membership data on December 31, 2019, the Church reported 20,946 members in 37 congregations, but this number doesn’t exceed 6,000 during the November 2020 census. As of October 4, 2020, a temple was announced to be constructed in Kiribati.
The only substantial non-Christian population is of the Baháʼí Faith. The Baháʼí Faith in Kiribati begins after 1916 with a mention by `Abdu'l-Bahá, then head of the religion, that Baháʼís should take the religion to the Gilbert Islands which form part of modern Kiribati. The first Baháʼís pioneered to the island of Abaiang (aka Charlotte Island, of the Gilbert Islands), on March 4, 1954. They encountered serious opposition from some Catholics on the islands and were eventually deported and the first convert banished to his home island. However, in one year there was a community of more than 200 Baháʼís and a Baháʼí Local Spiritual Assembly. Three years later the island where the first convert was sent to was found to now have 10 Baháʼís. By 1963 there were 14 assemblies.
As the Ellice Islands gained independence as Tuvalu and the Gilbert Islands and others formed Kiribati, the communities of Baháʼís also reformed into separate institutions of National Spiritual Assemblies in 1981. The Baháʼís had established a number schools by 1963 and there are still such today - indeed the Ootan Marawa Baháʼí Vocational Institute being the only teacher training institution for pre-school teachers in Kiribati. The census figures are consistently between 2 and 3% for the Baháʼís while the Baháʼís claim numbers above 17%. All together the Baháʼís now claim more than 10,000 local people have joined the religion over the last 50 years and there are 38 local spiritual assemblies.
The 2010 census listed smaller religions such as Te Koaua, Assembly of God, Church of God, and Islam as other options. There is also an All Nations Church with few followers (Ministries Without Borders). According to the Association of Religion Data Archives, there is a non-negligible population of Buddhists comprising less than 0.1% of the population. Unlike many Pacific Island countries, there was no significant Indian migration to Kiribati and in 1981, the Indian population comprised only 15 people, mostly expatriates on assignment from the Government of India. The main religions of the Indian families in Kiribati are Hinduism, Sikhism, and Christianity. On 30 October 1978, a Diwali festival was celebrated with a feast in the country. As of 2010, the Hindu population in Kiribati is still negligible.
The constitution of Kiribati provides for the freedom of religion, although it also states that this freedom may be overruled in the interests of public defense, safety, order, morality, or health, or to protect the rights of others. Most government ceremonies open and close with Christian prayer. The government also provides small development grants to religious organizations among other NGOs.
Any religious group representing more than 2 percent of the population (about 2160 people as of the 2015 census) must register with the government, although there are no penalties for failure to register.
There is no standardized religious education program in public schools, but schools generally allow representatives of various faiths to provide religious education courses.
Two islands in Kiribati, Arorae and Tamana, maintain a "one-church-only" tradition, refusing to build any religious structures other than a single church. According to officials, this custom is in deference to the Protestant missionaries that arrived on those islands in the 19th century. Residents of other religions on those islands are able to worship freely in their homes, and the government has received no reports of complaints about this policy.