Boas argued that anthropologists should make historical comparisons within well-defined regional contexts. A century later, we have many improvements in the statistical methodologies for comparative research, yet most of our regional constructs remain without a valid empirical basis. We present a new method for developing and testing regions. The method takes into account older anthropological concerns with relationships between culture history and the environment, embodied in the culture-area concept, as well as contemporary concerns with historical linkages of societies into world systems. We develop nine new regions based on social structural data and test them using data on 351 societies. We compare the new regions with Murdock's regional constructs and find that our regional classification is a strong improvement over Murdock's. In so doing we obtain evidence for the cross-cultural importance of gender and descent systems, for the importance of constraint relationships upon sociocultural systems, for the historical importance of two precapitalist world systems, and for strikingly different geographical alignments of cultural systems in the Old World and the Americas. © 1996 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved.