The New Testament is the second major part of the Christian biblical canon, the first part being the Old Testament. Although Christians hold different views from Jews about the Old Testament, Christians regard both the Old and New Testaments together as sacred scripture. The contents of the New Testament deal explicitly with first-century Christianity. Therefore, the New Testament (in whole or in part) has frequently accompanied the spread of Christianity around the world. It reflects and serves as a source for Christian theology and morality. Both extended readings and phrases directly from the New Testament are also incorporated (along with readings from the Old Testament) into the various Christian liturgies. The New Testament has influenced religious, philosophical, and political movements in Christendom, and left an indelible mark on its literature, art, and music.

The New Testament is an anthology, a collection of Christian works written in the common Greek language of the first century, at different times by various writers, who were early Jewish disciples of Jesus of Nazareth. In almost all Christian traditions today, the New Testament consists of 27 books. The original texts were written in the first and perhaps the second centuries of the Christian Era, generally believed to be in Koine Greek, which was the common language of the Eastern Mediterranean from the Conquests of Alexander the Great (335–323 BC) until the evolution of Byzantine Greek (c. 600). All of the works which would eventually be incorporated into the New Testament would seem to have been written no later than around AD 150.

Collections of related texts such as letters of the Apostle Paul (a major collection of which must have been made already by the early 2nd century) and the Canonical Gospels of Matthew, Mark, Luke, and John (asserted by Irenaeus of Lyon in the late-2nd century as the Four Gospels) gradually were joined to other collections and single works in different combinations to form various Christian canons of Scripture. Over time, some disputed books, such as the Book of Revelation and the Minor Catholic (General) Epistles were introduced into canons in which they were originally absent. Other works earlier held to be Scripture, such as 1 Clement, the Shepherd of Hermas, and the Diatessaron, were excluded from the New Testament. The Old Testament canon is not completely uniform among all major Christian groups including Roman Catholics, Protestants, the Greek Orthodox Church, the Slavic Orthodox Churches, and the Armenian Orthodox Church. However, the twenty-seven-book canon of the New Testament, at least since Late Antiquity, has been almost universally recognized within Christianity (see Development of the New Testament canon).

The New Testament consists of