The four gospels of the New Testament — Matthew, Mark, Luke and John — are the main source of information on the life of Jesus. For various reasons modern scholars are cautious of relying on them uncritically, but nevertheless they do provide a good idea of the public career of Jesus, and critical study can attempt to distinguish the original ideas of Jesus from those of the later authors.
The four canonical gospels, like the rest of the New Testament, were written in Greek, Mark probably c. AD 66–70, Matthew and Luke around AD 85–90, and John AD 90–110. Despite the traditional ascriptions, all four are anonymous, and none were written by eyewitnesses.
In the immediate aftermath of Jesus' death his followers expected him to return at any moment, certainly within their own lifetimes, and in consequence there was little motivation to write anything down for future generations, but as eyewitnesses began to die, and as the missionary needs of the church grew, there was an increasing demand and need for written versions of the founder's life and teachings. The stages of this process can be summarised as follows:
Mark, the first gospel to be written, uses a variety of sources, including conflict stories (Mark 2:1–3:6), apocalyptic discourse (4:1–35), and collections of sayings, although not the sayings gospel known as the Gospel of Thomas and probably not the Q source used by Matthew and Luke. The authors of Matthew and Luke, acting independently, used Mark for their narrative of Jesus's career, supplementing it with the collection of sayings called the Q document and additional material unique to each called the M source (Matthew) and the L source (Luke). Mark, Matthew and Luke are called the synoptic gospels because of the close similarities between them in terms of content, arrangement, and language. The author(s)/editor(s) of John may have known the synoptics, but did not use them in the way that Matthew and Luke used Mark. There is a near-consensus that this gospel had its origins as a "signs" source (or gospel) that circulated within the Johannine community (the community that produced John and the three epistles associated with the name), later expanded with a Passion narrative and a series of discourses.
All four also use the Jewish scriptures, by quoting or referencing passages, or by interpreting texts, or by alluding to or echoing biblical themes. Such use can be extensive: Mark's description of the Parousia (second coming) is made up almost entirely of quotations from scripture. Matthew is full of quotations and allusions, and although John uses scripture in a far less explicit manner, its influence is still pervasive. Their source was the Greek version of the scriptures, called the Septuagint - they do not seem familiar with the original Hebrew.