The most common explanation for the material shared by Matthew and Luke (the double tradition) is that Matthew and Luke both used a source now lost, called Q. If we adopt the Q hypothesis to account for the double tradition, then what theory best accounts for the material that Matthew and Luke share with Mark? Three main theories have been proposed: Matthew and Luke used the Gospel of Mark as a source (the standard theory of Markan priority), Matthew and Luke used a revised version of Mark's gospel (the Deutero-Mark hypothesis), or all three evangelists used a source similar to, but earlier than, the Gospel of Mark (the Proto-Mark hypothesis). Delbert Burkett provides new data that calls into question the standard theory of Markan priority and the Deutero-Mark hypothesis. He offers the most comprehensive case to date for the Proto-Mark hypothesis, concluding that this theory best accounts for the Markan material.