This article seeks to resource contemporary discussions about divine simplicity by exploring how this doctrine was understood throughout patristic and medieval church history, especially with respect to the relation of divine simplicity to the doctrine of the Trinity. It argues, first, that there have been different versions of divine simplicity throughout church history, though most current treatments focus on the Thomist version. Second, it suggests that divine simplicity had a greater role in the witness and worship of the church than is generally recognized today. Third, it argues that many of the differences between contemporary and ancient treatments of divine simplicity boil down to more basic ontological differences. Finally, it draws attention to the close connection between divine simplicity and the Trinity throughout church history, and suggests that the doctrine of divine simplicity provides a more reliable means of grounding the Trinity as monotheistic than the doctrine of perichoresis.Since the publication of Alvin Plantinga's Does God Have a Nature? 1 in 1980, the doctrine of divine simplicity has received a significant increase of attention from a number of philosophers and theologians. Much of the recent treatment of divine simplicity has been critical. A wide variety of arguments have been raised against divine simplicity, including: (1) abstract properties cannot be identified with a concrete, personal God; 2 (2) if God is identical to his properties, his properties are all * Historical Theology, Fuller Theological Seminary,