This essay discusses conceptual issues that arise from the study of human social change. The comparative and evolutionary world-systems perspective is explained as a theoretical research program for studying long-term social change. This approach employs an anthropological framework of comparison for studying world-systems, including those of hunter-gatherers. Problems of spatially bounding whole human interaction networks are addressed, and the utility of a comparative approach to the study of hierarchical relations among human polities (core/periphery relations) is examined. The hypothesis of semiperipheral development is explained, and criteria for empirically identifying semiperipheral regions are specified. World history and global history are the most important evidential bases, along with prehistoric archaeology, for the comparative study of world-systems. Getting the grounds of comparison right by correctly conceptualizing the spatial units of analysis and paying careful attention to core/periphery relations are crucial issues in the effort to comprehend and explain the development of world-systems.