The gospels usually refer to the first four books of the New Testament: Matthew, Mark, Luke, and John. They are the primary books of the Bible that narrate the life of Jesus. They are also the closest thing we have to good historical sources about Jesus.
Various other apocryphal gospels exist but were not selected for inclusion in the Bible. Though the historical value of the canonical Gospels is highly debatable, scholars judge that the non-canonical gospels are even less likely to be historical.
Since the 2nd century, Christians have claimed that the gospels were written by Jesus' disciples and their companions. Matthew and John were alleged to have been written by those members of the twelve, Mark was alleged to have been written by Peter's secretary, and Luke was alleged to have been written by Paul's physician. Modern scholarship, however, has called these claims into question.
Attempts by modern apologists to defend the eyewitness status of the gospels often betray an ignorance of basic Biblical scholarship. For example, it is claimed that II Peter 1:16 shows that the New Testament was written by eyewitnesses. However, the books of the New Testament were originally circulated independent of one another, so even if II Peter were written by an eyewitness to Jesus' ministry, it would have no bearing on the authorship of the gospels. Furthermore, a close comparison of II Peter to the epistle of Jude shows that the author of II Peter plagarized Jude, and for this reason, among others, scholars have almost unanimously concluded that II Peter is not authentic.
One reason for doubting the traditional gospel authorship claims is that it seems the gospels were originally anonymous. This fact is accepted even by very conservative scholars such as Craig Blomberg. For one, the titles gospel manuscripts we have say things like "according to Matthew" rather than "by Matthew." Another reason for this conclusion is that they are discrepencies between manuscripts, a clear indication that the titles were later additions.
In his Introduction to the New Testament, scholar Raymond Brown gives reasons for doubting the authorship of individual gospels:
- Matthew seems to have copied from Mark as well as a no longer extant document that scholars have labled Q. It seems unlikely that an actual eyewitness would follow such a procedure.
- Christian tradition indicates John Mark was a Palestinian Jew, but the Gospel of Mark is written in Greek and does not seem to be a translation from Aramaic. The book also has problems in geography and seems to have been based on traditions that circulated in Greek.
- The book of Acts was apparently written by the same person as Luke, and seems to contradict Paul's letters on some points.
- John's mention of a "beloved disciple" does not refer to the actual author of the book, but rather to the ultimate source of its traditions.
These considerations are enough for Brown to totally reject the traditional claims for Matthew, Mark, and John, though he says it is "not impossible" that the author of Luke was a minor companion of Paul. Brown's verdict on this issue is noteworthy because he was a fairly conventional Catholic who sharply criticized the idea that the gospels' supernatural elements deserve special skepticism. This debunks the claim, sometimes made by apologists, that scholars reject the traditional authorship claims simply because they assume miracles cannot happen.
For these reasons, it is safe to conclude that the gospels are hearsay. They are not the sort of evidence that would be allowed into a court of law. Though they may contain some historical information, their historical reliability is not well enough established for them to be used to prove Jesus' miracles actually occurred, as some Christian apologists claim. It is likely the actual authors of the gospels were Christians in the early church who invented the idea of the resurrection and divinity of Jesus to suit their agenda of gaining converts. This manipulation of the New Testament occurred progressively and begin in the 1st century .
Mainstream scholars conjecture that the gospels were written sometime between 66 A.D. and 110 A.D., with Mark being written first and John being written last. Conservatives argue that Luke/Acts must have been written before Paul's death c. 64 A.D. because it does not mention the event. This would imply that Mark was written even earlier, because Luke appears to have copied from Mark. However, it seems Luke/Acts was designed to pitch Christianity to Gentiles, and if this were the case it would make sense to end with Paul's declaration that Jesus came to save Gentiles rather than the unfortunate fact of Paul's death at gentile hands.
In 1972, paleographer Jose O'Callaghan claimed to have found a fragment of the Gospel of Mark that could be dated no later than 50 A.D. However, this claim was based on only a few letters worth of legible text. Most scholars see O'Callaghan's claim as insufficient reason to date Mark earlier than what is currently accepted.
Even if the first gospels were written in the late 50's or early 60's, we would still have a gap of about three decades between the events recorded and their composition. Apologists regularly claim that even by mainstream dating, the gospels were written too early to contain any legendary components. However, numerous counter examples to this claim can be given. In the early 90's, scholar Robert M. Price produced an essay citing numerous examples of legends that sprang up very quickly regarding figures ranging from Sabat Sevi to Charles Manson. 
A common argument for the reliability of the gospels is that we have many manuscript copies of them. As an argument for the historical reliability of the texts, this is a non-sequitur: making a million copies of a lie will not turn it into a truth. As an argument for the text of the gospels we have today being true to the originals, this argument does have some validity. Our ability to reconstruct the original text of the gospels is much better than for many other ancient documents. However, comparisons of the different gospel manuscripts do reveal discrepencies. Most of these are minor, but there are two places in which large passages seem to be much later additions to the text: Mark 16:8-12 and John 7:53-8:11 . Worse, with the exception of two tiny fragments, all of our gospels manuscripts date from after c. 200 A.D. This means we are in no position to detect any tampering that occured prior to this date. It should be noted that while this situation is troubling to some believers in Biblical inerrancy, it is not the most serious problem with the historical reliability of the gospels. The problem of legendary embellishment is much larger. Also, contrary to what popular sources such as The Da Vinci Code claim, there is no evidence of large-scale rewriting of the Bible in the era of Constantine.
Because thte gospels present four accounts of the same alleged historical events, the opportunity for contradictions on matters of historical detail is arguably greater than anywhere else in the Bible. The opportunity is by no means a missed one. Some of the most serious contradictions:
- John presents a radically different portrait of Jesus than the first three gospels. It is the source of much important Christian theology, but because it was written later than the other three books, scholars judge that it is much less likely to contain historical information.
- Matthew and Luke both trace Jesus' genealogy back to King David, but the two genealogies contradict eachother. Likely, both were invented to satisfy the expectation that the Messiah would be descended from David. Christians have made numerous attempts to harmonize these contradictions, but these tend to fly in the face of known facts, i.e. by claiming that one genealogy goes through Mary when both explicitly trace Jesus' descent through Joseph. Modern investigators are fortunate that the authors apparently were not comparing notes.
- Matthew and Luke tell different stories of Jesus' birth. The standard birth narrative presented in movies, Christmas pageants, etc. combines details of both stories without being entirely Biblically accurate. The reason for this is that attempts to harmonize the two stories are implausible at best. Interestingly, both stories serve the purpose of explaining how it came to be that Jesus was born in Bethlehem but grew up in Nazereth. The most likely explanation is that Jesus was born in Nazareth and that the birth narratives were invented in response to the belief that the Messiah would be born in Bethlehem. Again, the authors do not seem to have been comparing notes.
- Blomberg, Craig. "The Historical Reliablity of the New Testament." in Reasonable Faith by William Lane Craig. Crossway Books, 1994. pp. 193-232.
- Brown, Raymond E. An Introduction to the New Testament. Doubleday, 1997.
- Ehrman, Bart. Jesus: Apocalyptic Prophet of the New Millenium. Oxford University Press, 1999.
- Ehrman, Bart. Misquoting Jesus: The Story Behind Who Changed the Bible and Why. HarperSan Francisco, 2005.
- Geisler, Norman. Baker Encyclopedia of Christian Apologetics. Bake Academic, 1999.
- McDowell, Josh. The New Evidence that Demands a Verdict. Thomas Nelson Publishers, 1999.