Christianity (from Latin Christianismus, and this from Greek χριστιανισμός)2 is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. It is the largest religion in the world, with an estimated 2.4 billion followers, with Catholicism being the Christian confession with the most followers (1.39 billion followers). 

It is a religion that is both culturally and doctrinally diverse. Its main branches are Catholicism, Protestantism, and Orthodoxy. Its adherents, called Christians, share the belief that Jesus of Nazareth is the Son of God and the Messiah (Greek: Christ) prophesied in the Old Testament and that he suffered, was crucified, descended into hell, and rose from the dead for the salvation of mankind. It emerged from Judaism in the mid-1st century AD in the Roman province of Judea. In its early decades, Christianity was regarded by some as a sectarian doctrine of Orthodox Jewish traditions.

The earliest leaders of Christian communities were the apostles and their successors the apostolic fathers. This early Christianity spread, despite being a minority and persecuted religion, throughout Judea, Syria, Europe, Anatolia, Mesopotamia, Transcaucasia, Egypt and Ethiopia. During these first centuries, the Fathers of the Church gradually consolidated the doctrines of Christianity and elaborated the canon of the New Testament.

Some of the sacred Christian writings are shared with Judaism. The Tanakh constitutes, together with the Greek Bible older than the Tanakh in its current form—the basis and source for the Old Testament of the different Christian Bibles. For this reason, Christianity is considered an Abrahamic religion, together with Judaism and Islam.

In the context of early Christianity, after the death of Stephen (the first Christian martyr) and even more so after the destruction of the Temple of Jerusalem in 70 by the Romans, two processes began: that of the progressive separation of early Christianity and rabbinical Judaism and that of the spread of Christianity, as can be seen in the first centers of Christianity. The followers of Jesus were first given the name "Christians" in Antioch, a place where, through the preaching of several disciples (such as Paul and Barnabas), there were many new followers.16 Christian doctrine since the times when there was a single Catholic Fraternal faith, has affirmed that Jesus founded a hierarchically organized and authoritative Christian community, led by the apostles (the first of whom was Simon Peter).

Later (according to the Acts of the Apostles), the apostles and early followers of Jesus structured an organized Church. A letter written shortly after 100 by Ignatius of Antioch to the Smyrnaeans (chapter 8) is the earliest surviving text in which the term ἡ καθολική ἐκκλησία (the catholic or universal Church) is used.