In this paper, we present a diachronic analysis of obsidian procurement patterns during the Postclassic period in the Lower R�o Verde region of Oaxaca. The study is based on x-ray fluorescence (XRF) and visual analysis of obsidian artifacts from excavated household contexts at Early Postclassic (a.d. 800–1100) R�o Viejo and Late Postclassic (a.d. 1100–1522) Tututepec (Yucu Dzaa). We report the presence of at least six sources of obsidian imported to the lower R�o Verde region in the Early Postclassic, whereas during the fourteenth and fifteenth centuries of the Late Postclassic, the local assemblage was dominated by obsidian from Pico de Orizaba and Pachuca. Changes in obsidian procurement patterns in the lower R�o Verde region through time are interpreted in light of sociopolitical change at the local, regional, and macroregional scales. The study represents the most detailed analysis of Postclassic period obsidian exchange yet reported from Oaxaca.