In this book, Ramsey theoretic methods introduced by Lachlan are applied to classify the countable homogeneous directed graphs. This is an uncountable collection, and this book presents the first explicit classification result covering an uncountable family. The author's aim is to demonstrate the potential of Lachlan's method for systematic use. It features: interface between combinatorics and model theory; unusual use of Ramsey's theorem to classify structures; an extension of an already elaborate branch of model theory; and the first monograph on Lachlan's method.