Starting with the fact that John of Antioch and Nestorius were friends, this article asks whether they were also theological allies, as is commonly assumed. Based on an examination of a letter written by John to Nestorius in November of ad 430, as well as other pertinent letters and documents, the author concludes that the two were not on the same side theologically, but that John was unaware of how fundamentally they disagreed. The relationship between John and Nestorius is then used to help interpret the proceedings at Ephesus in ad 431, the action of John and of Cyril of Alexandria in the Reunion of 433 and the Christological controversy as a whole.