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

The term born again has its origin in the New Testament. In his first epistle, Apostle Peter describes the new birth as taking place from the seed which is the Word of God. (Being born again, not of corruptible seed, but of incorruptible, by the word of God. 1 Peter 1:23) In the gospel of Luke, Jesus himself refers to the Word of God as the seed. (The seed is the Word of God. Luke 8:11)

In contemporary Christian usage and apart from evangelicalism, the term is distinct from similar terms which are sometimes used in Christianity in reference to a person who is being or becoming a Christian. This usage of the term 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 practice is based on the belief that non-Evangelical Christians, even those Christians who are professed Christians, are not "born again" and do not have a "personal relationship with Jesus." They therefore believe that they should evangelize to non-Evangelical Christians in the same way that they would evangelize to people 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, and it is also used as an adjective to describe the movement itself ("born-again Christian" and the "born-again movement").