The Palaeozoic geological history of western South America has been the focus of intense international interest in the last few years. This book brings together multidisciplinary research and review papers on the Lower Palaeozoic geology of the Sierras Pampeanas and the Precordillera of central west Argentina. It deals with the final stages of assembly of the supercontinent of Gondwana and a period of tectonic interaction with Laurentia (the North American continent of today). The evidence for the growth of this part of the margin of Gondwana from late Neoproterozoic times is presented in terms of stratigraphy, palaeontology, igneous petrology, geochemistry and geochronology, and rival tectonic hypothesis are critically compared. At least two episodes of subduction-related marginal basin closure and terrane accretion are documented and re-assessed.