See The Lost Books of the Bible and the Forgotten Books of Eden (Collins-World, 1977), especially the introduction by Frank Crane. The book actually contains a selection of well-known materials including the Apostolic Fathers, the Odes of Solomon and the Proto-Evangelium Jacobi.

The term “Christian Apocrypha” is gaining favor over the older term “New Testament Apocrypha” for a number of reasons; one is that most of the Christian Apocrypha were alive and strong in the church before there was a New Testament.