Constitutional political economy is a research program that directs inquiry to the working properties of rules, and institutions within which individuals interact, and the processes through which these rules and institutions are chosen or come into being. The emphasis on the choice of constraints distinguishes this research program from conventional economics, while the emphasis on cooperative rather than conflictual interaction distinguishes the program from much of conventional political science. Methodological individualism and rational choice may be identified as elements in the hard core of the research program. Copyright George Mason University 1990