Religious conversion is the adoption of a new religious identity, or a change from one religious identity to another. This typically entails the sincere avowal of a new belief system, but may also present itself in other ways, such as adoption into an identity group or spiritual lineage. "Conversion" occurs not only from one religion to another, but also between different denominations within the same faith, when this involves a felt change of identity rather than other reasons such as convenience.

Types of religious conversion include:

• Marital conversion, religious conversion upon marriage outside of religion
• Secondary conversion, done because of a personal relationship
• Deathbed conversion, the acceptance of religious belief shortly before death.
• Forced conversion, done under threat - a form of religious persecution

Christianity and Islam are major religions which emphasize the desirability of conversion. Buddhism has done so historically, and still witnesses modest levels of missionary activity. Judaism and Hinduism allow in-conversion, but generally do not encourage it.

Proselytism is the act of attempting to convert another individual from a specific religion or belief system. (See proselyte).

Apostate (n.) is a term with pejorative connotations used by members of one church or religion to refer to someone who has left that church or religion.

Conversion to Christianity

main: Christianization

main: List of converts to Christianity thumb|220px|The Augsburg Confession divides repentance into two parts: "One is contrition, that is, terrors smiting the conscience through the knowledge of sin; the other is faith, which is born of the Gospel, or of absolution, and believes that for Christ's sake, sins are forgiven, comforts the conscience, and delivers it from terrors." Conversion to Christianity is the religious conversion of a previously non-Christian person to some form of Christianity. The exact understanding of what it means to attain salvation varies somewhat among denominations. It primarily involves repentance of sin, baptism in the name of Father, Son and Holy Spirit, and a decision to live a life that is holy and acceptable to God.

Within the Christian faith, conversion is intended to involve more than a simple change in religious identity. In fact, the Latin word conversio, translating the Greek metanoia, literally means "going the other way." The convert, therefore, is expected to renounce sin and personally commit to a life of righteousness as described by Paul of Tarsus and exemplified by Jesus. In some Protestant traditions, this is called "accepting Christ as one's Savior and following him as Lord."BibleGateway.com- Commentaries » Matthew 16 » The Cost of the Kingdom