That having been said, the letter of James could have been written anytime between 40 and 60 A.D., but I tend to date it early because it is simple and primitive in its Christology and Theology, and it is addressed to the Twelve Tribes of Israel in the Diaspora.
Additionally, Matthew seems to use James liberally in composing the Sermon on the Mount, which is a blend of Luke's Sermon on the Plain and James, as well as other collected sayings of Jesus, now removed from their original historical context:
|I didn't see the Gospels on there, when were they written?|
Peter would have had access to this, and would have assisted Mark to write the first near-complete Gospel (either Mark or Ur-Mark), probably sometime before Paul came to Rome (50s?).
Luke seems to have used Mark as a base, and combined it with Matthew's sayings collection, as well as eyewitness accounts from other early Apostolic church members, sometime before 60 A.D. (Luke was written before Acts, c. 60-62 A.D.).
|Luke block-copies Mark||Matthew block-copies Mark|
Mark may have been revised after the composition of Luke, since Luke omits one large section of our current version of Mark, (the Great Lukan Omission, Mark 6:45-8:25).
Our Greek Matthew seems to have been composed on the same general idea as Luke (combining Mark with other sayings material). However, Matthew clearly uses the version of Mark now containing the Lukan Omission section.
Matthew was apparently composed sometime after controversies between Jewish Christians and Gentile Christians had been worked out, as he has carefully combined Luke's Sermon on the Plain and the letter of James to produce his opus "Sermont on the Mount", a large and organized collection of many of Jesus' sayings, now blended with James' teaching and lacking most of the original contexts, which are given in Luke and Mark etc.
Matthew is also the only Gospel to use the word "Church" (ekklesia), and was probably written just after Luke, possibly in the 60s, after the Church had finally split with the Jewish community; but apparently before the destruction of Jerusalem.
For more info on the Synoptic Problem, go to our website here, for good diagrams etc: