Born again, or to experience the new birth, is a phrase, particularly in evangelicalism, that refers to "spiritual rebirth", or a regeneration of the human spirit. In contrast to one's physical birth, being "born again" is caused distinctly and separately by baptism in Holy Spirit, not by baptism in water. It is a core doctrine of the denominations of the Methodist, Quaker, Baptist, and Pentecostal Church along with all other evangelical Christian denominations. All of these strongly believe Jesus' words in the Gospels: "You must be born again before you can see, or enter, the Kingdom of Heaven." Their doctrine also mandates that to be both "born again" and "saved" one must have a personal and intimate relationship with Jesus Christ.

In contemporary Christian usage, the term is distinct from the sometimes similar terms used in Christianity apart from evangelicalism to refer to being or becoming a Christian. This is usually linked to baptism with water and the related doctrine of baptismal regeneration. Individuals who profess to be "born again" (meaning in the "Holy Spirit") often state that they have a "personal relationship with Jesus Christ".

In addition to using this phrase with those who do not profess to be Christians, some Evangelical Christians use the phrase and evangelize those who belong to other Christian denominations or groups. This is based on a belief that non-Evangelical Christians, even those who are professed Christians, are not "born again" and do not have a "personal relationship with Jesus." They therefore believe they should evangelize non-Evangelical Christians the same way they would evangelize those who do not profess the Christian faith.

The phrase "born again" is also used as an adjective to describe individual members of the movement who espouse this belief, as well as the movement itself ("born-again Christian" and the "born-again movement").