In this landmark study of the literary relationship between the gospel of John and the synoptic gospels, Gary Greenberg presents compelling evidence for the existence of a written pre-canonical Alpha gospel that contained almost all of the main episodes in the adult life of Jesus (excluding major speeches, such as discourses, parables, and "I Am" sayings) and which became the written source for the core biography of Jesus in Mark, Luke, John, and Matthew. While Mark used the Alpha gospel with only slight variations, John had profound theological disagreements with it, objecting to its theological message about how to obtain eternal life, the depiction of Jesus, and other matters. This induced him to rewrite the Alpha gospel so that it conformed to his own very different theological agenda. Consequently, John's gospel functions as a thorough theological critique of Mark, but the changes he introduced made it difficult to see how he and Mark worked from the same written source. By using John's theological concerns as a filter for reading and understanding what objections John would have with Mark's Jesus stories, The Case for a Proto-Gospel reverse-engineers the editorial path taken by John and reconstructs the content of the Alpha gospel. Finally, the author discusses the relationship of the other two synoptic gospels to the Alpha gospel, asserting that Luke also knew the Alpha gospel but used Mark as his primary source, and that while Matthew did not know the Alpha gospel, his use of Mark as a primary source ensured that his core biography of Jesus also derived from this earlier source.