The Chaco Mission Frontier is a welcome addition to the growing corpus of anthropologically informed, documented histories of missions in the Americas. James Saeger’s expertise focuses on the interior lowlands of South America, in particular, the riverine and plains environment of the Chaco, lying in the modern nations of Paraguay, Argentina, and a small portion of southeastern Bolivia. The Guaycurúan ethnic bands who people Saeger’s story, unlike their better-known Guaraní cousins, were principally hunter-gatherers who managed and derived their subsistence from the semiarid environment of the Chaco. Throughout the detailed, descriptive chapters that focus both thematically and chronologically on economy, society, politics, and religion, Saeger reveals his thorough knowledge of the region, its geography, and its archives. This book is an attempt to evaluate the mission as an institution as much as it is an ethnohistory of the Guaycurúan peoples and cultures that provide the substance of Saeger’s study.The Chaco Mission Frontier presents two parallel, central arguments: first, it addresses the issue of change and continuity in the Guaycurúan’s colonial experience before and after entering mission reductions; secondly, it enters the debate on whether the missions were oppressive of the indigenous peoples who lived in them and destructive of their cultures, or vehicles for the survival of native communities and for new cultural formations. On the first point, Saeger argues cogently for continuity, stressing that the Guaycurúans who settled in Jesuit missions during the second quarter of the eighteenth century had already experienced gradual but irreversible changes in their material culture and environment, due mainly to the introduction of European livestock and to their own hunting for trade. Thus, mission communities provided a setting for Mocobis, Abipones, Mbayás, Tobas and other groups to sustain their already altered cultural practices. His examination of the economic life crafted by missionaries and Guaycurúans systematically considers different skills and types of labor performed by both men and women in terms of the points of continuity with pre-mission lifeways. Guaycurúan raiding and warfare never ceased and, together with native mobility, conditioned the mission experience.Saeger built the concluding chapter of the book around a thoughtful dialogue with David Sweet’s essay, “The Ibero-American Frontier Mission in Native American History” published in E. Langer and R. Jackson, eds., The New Latin American Mission History (1995). Sweet raised a forceful challenge to traditional epic treatments of missions as civilizing institutions, emphasizing more recent findings of demographic decline, “infantilization,” “deculturation,” and separation of indigenous peoples from their natural environment. Saeger argues cogently that conquest and missionization should not be conflated, and revisits Sweet’s revisionist salvo with a point-by-point comparison with his findings specifically on the Chaco missions of the Guaycurú, noting that a number of Sweet’s arguments are not factually or interpretively applicable to his case. This raises the question of Guaycurúan exceptionalism in reference, for example, to the relatively late periodization of these missions and the physical mobility of their neophytes. Saeger does not, however, engage the wider historiographical context established by the substantial literature published during the last two decades on missions throughout the Americas, nor does he draw comparisons with histories of colonial missions in other areas of the world on such issues as conversion and ethnic identity.Saeger frequently raises descriptive comparisons with, for example, Plains Indians of North America, in terms of trading and raiding patterns, or nineteeth-century governmental policies of assimilation or containment. These particular references, while informative, do not constitute a comparative matrix nor are they geographically or thematically consistent. Frontier, despite its prominent place in the book’s title, is not treated analytically in this study, in reference either to the intersecting boundaries of Spanish and Portuguese imperialism or to the transitional ecological and cultural zones of the Gran Chaco. Saeger’s findings will contribute, however, to future synthetic treatments of frontiers and borderlands in the Americas.