Religious conversion is the adoption of a new religion that differs from the convert's previous religion. Changing from one denomination to another within the same religion (e.g., Christian Baptist to Methodist or Catholic,Muslim Shi'a to Sunni, etc.) is often described as conversion.

People convert to a different religion for various reasons, including: active conversion by free choice due to a change in beliefs,secondary conversion, deathbed conversion, conversion for convenience and marital conversion, and forced conversion.

Conversion or reaffiliation for convenience is an insincere act, sometimes for relatively trivial reasons such as a parent converting to enable a child to be admitted to a good school associated with a religion, or a person adopting a religion more in keeping with the social class he or she aspires to. When people marry one spouse may convert to the religion of the other.

Forced conversion is adoption under duress of a different religion. The convert may secretly retain the previous beliefs and continue, covertly, with the practices of the original religion, while outwardly maintaining the forms of the new religion. Over generations a family forced against their will to convert may wholeheartedly adopt the new religion.

Blessed Mother Teresa of Calcutta (Albanian: Nënë Tereza) as she is known to the Catholic Church, or Mother Teresa as she is commonly known, was born Agnes Gonxha Bojaxhiu (pronounced [aɡˈnɛs ˈɡɔndʒa bɔjaˈdʒiu]). Although born on the 26 August 1910, she considered 27 August, the day she was baptized, to be her "true birthday". “By blood, I am Albanian. By citizenship, an Indian. By faith, I am a Catholic nun. As to my calling, I belong to the world. As to my heart, I belong entirely to the Heart of Jesus.” Mother Teresa died on 5 September 1997 and is not yet a Catholic Saint. In late 2003, the leaders of the church completed the process of beatification, the third step toward possible sainthood. A second miracle credited to Mother Teresa is required before she can be recognized as a saint by the Catholic church.

Mother Teresa founded the Missionaries of Charity, a Roman Catholic religious congregation, which in 2012 consisted of over 4,500 sisters and is active in 133 countries. Members of the order must adhere to the vows of chastity, poverty and obedience, and the fourth vow, to give "Wholehearted and Free service to the poorest of the poor". The Missionaries of Charity at the time of her death had 610 missions in 123 countries including hospices and homes for people with HIV/AIDS, leprosy and tuberculosis, soup kitchens, children's and family counselling programmes, orphanages and schools.