In his work, Nicaea and Its Legacy, Lewis Ayres raises a number of issues important to the discipline of theology. The first is simply the difficulty of studying the past, especially the fourth century, one of the key periods in the formation of Christian theology. Reading texts from fifteen hundred years ago is sufficiently challenging, but these texts are set in a very complex history (or histories) of theological, social and imperial controversies and transitions. Then there is the task of relating the study of historical theology to modern systematic theology, knowing that simply retelling the history more thoroughly will not solve or resolve modern issues, for they have their own complicated genealogy. There is also the need to be aware of the involvement of different exegetical practices and presuppositions—then and now—in all of this. Finally, and most broadly or ecumenically, there are the implications that such work now has for dialogue between “Western” and “Eastern” trinitarian theology, and the questionable usefulness of such categories. That Ayres has remained sensitive to these, and other, dimensions of difficulty, while also engaging with a substantial body of literature, numerous primary texts, and diverse secondary texts (if that is still a useful distinction) makes his work both challenging and significant.