The first step was Judaism's canonisation of the Hebrew Bible. During the fourth to second century BCE, the Law (Torah, known to Christians as the Pentateuch) reached final form and canonical status. Prior to the Council of Jamnia, which appeared to have taken place around 90 CE, there does not seem to have been a Jewish concept of one Bible. The Council is believed to have finally defined the Jewish canon, except for the Ethiopina Jews who do not accept the Council's legitimacy. However, some scholars have recently suggested that the Council was not about canonicity at all, asserting that they were actually dealing with other concerns entirely.
By the fourth century, the Christian church began to concern itself about exactly what Old Testament books should be included, and Bishop Melito of Sardis went to Palestine to discover which Hebrew books belonged in the canon.
The first to unmistakably quote the New Testament as scripture, "as it is written," seems to have been Basilides, a gnostic teacher at Alexandria in the first part of the second century CE. And the first to use the term, "New Testament," was Irenaeus, who flourished about 180 CE. He is also the first to give the explicit formation of four gospels, and exactly four. In fact, the Gospels According to Matthew, Mark, Luke and John were never mentioned together until 180 CE. The canon of Muratori, a Roman document of the second half of the second century, states that what the apostle Paul wrote to the Christians of a particular church is meant for all. This inspired the canonisation of the Epistles.
Bishop Eusebius of Caesaria, a leading church historian in the fourth century, wrote, "It will be well, at this point, to classify the New Testament writings. We must, of course, put first the holy quartet of the Gospels, followed by the Acts of the Apostles. The next place in the list goes to Paul's Epistles, and after them we must recognise the Epistle called 1 John, likewise 1 Peter. To these may be added, if thought proper, the Revelation of John …. These are classed as Recognised Books. Those that are disputed, yet familiar to most, include the Epistles known as James, Jude, and 2 Peter, and those called 2 and 3 John, either the work of the evangelist or of someone else with the same name." Eusebius apparently also listed 1 Clement in his canon, and considered Hebrews a disputed book.
The New Testament, as we now know it, was formally accepted by a council at Rome in 382.
The sixteenth century Council of Trent finally established the Catholic Old Testament canon, in response to Protestant arguments. The sixteenth century was really the point at which Catholic and Protestant Churches all identified exactly what books were regarded as forming the Bible.