Q source
Ever since the Augustinian hypothesis, scholars continue to debate the order in which the gospels were written, and how they may have influenced each other, and several hypothesis exist in that regard, e.g. the Markan priority hypothesis holds that the Gospel of Mark was written first c. 70 CE. In this approach, Matthew is placed at being sometime after this date and Luke is thought to have been written between 70 and 100 CE. However, according to the competing, and more popular, Q source hypothesis, the gospels were not independently written, but were derived from a common source called Q. The two-source hypothesis then proposes that the authors of Matthew and Luke drew on the Gospel of Mark as well as on Q.