This book, the first of a projected three, reports on excavations at Formative-period sites in the state of Tlaxcala, Mexico. The transition to the Formative in the relatively high-altitude study region is later than in choice regions for early agriculture elsewhere in Mesoamerica. From 900 BC, however, population growth and sociopolitical development were rapid. A central claim in the research presented here is that a macroregional perspective is essential for understanding the local Formative sequence. In this volume, excavations at three village sites (Amomoloc, Tetel, and Las Mesitas) and one modest regional center (La Laguna) are reported. Ceramics are described in detail. An innovative approach to the classification of figurines is presented, and a Formative chronology for the region is proposed based on seriation of refuse contexts and radiocarbon dates. The work concludes with a macroregional framework to be used in the analysis of subsistence, social relations, and political economy in forthcoming volumes 2 and 3.