Given the central role of the concept of material capabilities in international politics models, and the ambiguity of the notion, it is essential that we define and measure it in operational terms. Such efforts have a long history and, given the multiplicity of interpretations as well as the difficulty of validation, we can expect alternative indicators to be put forth with some regularity well into the future. Herein, some of the assumptions, procedures, and implications of the Correlates of War project effort. First, we treat “power” as the generic concept, defined as the capacity of a state (or other actor) both to exercise influence and to resist influence attempts. That capacity is a function of, inter alia, geography, political organization and legitimacy, definition of “interests,” elite competence, and, of course, material capabilities. We see the last of these as falling along three dimensions: demographic, industrial, and military. The paper spells out the measurement problems, theoretic premises, data sources, and combinatorial options of this dataset on national capabilities.