The doctrine of the Trinity is the keystone of Christian faith and teaching, yet most of the secondary accounts on the development of this crucial doctrine do not extend beyond Nicaea and pay scant attention to vital cultural traffic. In this volume, the author examines the exposition of the doctrine of the Trinity in a set of texts from key Arabic Christian thinkers from the eighth and ninth centuries and demonstrates that fresh thinking of this cornerstone doctrine occurred in the new context of a regnant Islamic culture; in this context, Christian theologians discovered the salience of the Nicene doctrine while engaging a new religious partner. The author provides an overlooked angle on the history of Trinitarian theology and brings attention to several profound Christian figures rarely found in Western accounts.