This article sheds new light on a crucial moment in the emerging Christological controversy. Among the key developments that occurred between 360 and the early 380s, the Christological debate between Apollinarius of Laodicea and Diodore of Tarsus made a significant, though largely misunderstood, impact on the Christological works of Gregory of Nazianzus. The article first characterizes the main Christological concerns of Apollinarius and Diodore and identifies the points of contention between them. It then gives a new interpretation of Gregory's relationship to this debate. It argues, finally, that Gregory Nazianzen defines his Christology chiefly in opposition to Diodore, rather than to Apollinarius, as is commonly believed, even as he opposes them both in the end. This article sheds new light on a crucial moment in the emerging Christological controversy. Among the key developments that occurred between 360 and the early 380s, the Christological debate between Apollinarius of Laodicea and Diodore of Tarsus made a significant, though largely misunderstood, impact on the Christological works of Gregory of Nazianzus. The article first characterizes the main Christological concerns of Apollinarius and Diodore and identifies the points of contention between them. It then gives a new interpretation of Gregory's relationship to this debate. It argues, finally, that Gregory Nazianzen defines his Christology chiefly in opposition to Diodore, rather than to Apollinarius, as is commonly believed, even as he opposes them both in the end.