The high-grade mineral ores of the Phnom Dek region in central Cambodia have long been suspected of playing a major role in the rise of Angkor, the largest medieval polity in mainland Southeast Asia. This article presents the first comprehensive study by the Industries of Angkor Project (INDAP) to document the extent of industrial activity in this region and test this important relationship. Using a combination of intensive field survey, surface collection, and archaeometallurgical analysis, we evaluate the temporal and spatial patterning of iron production and the heterogeneity of smelting systems. The identification of at least three different smelting traditions has a significant impact on the current view that twentieth-century Kuay smelting practices extend deep into Cambodia’s history, and their relationship with Angkor in particular. More broadly, the survey demonstrates the importance of Phnom Dek as a major production zone on par with more well-known examples in Roman Europe and Africa.