This article presents the chronological framework used to reconstruct the political history of the ancient Lowland Maya site of Xunantunich in the upper Belize River valley. Extensive excavations from 1991 to 1997 by the Xunantunich Archaeological Project produced the ceramic, architectural, and epigraphic data needed to place the site within a temporal context. Refinement of the Barton Ramie ceramic chronology was the first step toward clarifying the Xunantunich chronology. Seriation of well-known Spanish Lookout types and modes from stratified deposits established a framework for understanding Late and Terminal Classic assemblages. Twenty-two radiocarbon samples place these ceramic complexes in absolute time. Obsidian hydration and masonry techniques were found to be less reliable chronological markers. The results indicate that Xunantunich emerged as a regional center during the Samal (A.D. 600–670) and Hats' Chaak (A.D. 670–780) phases of the Late Classic period. Arguably, this rapid growth and florescence was initiated under the auspices of nearby Naranjo. Although the polity achieved political autonomy in the following Tsak' phase (A.D. 780–890) of the Terminal Classic period, civic construction diminished and rural populations declined until the site collapsed sometime during the late ninth or early tenth century.