Introduction In this chapter there is a shift from states to individuals as actors and a focus on their belief systems, emotions, motivations, and risk orientations. This focus involves a theoretical move from the substantive rationality theorem to the bounded rationality theorem in the specification of the realist and game theory models introduced in Chapter 2, which analyze the exercise of power by leaders in making foreign policy decisions. The analytical approach in the present chapter of describing and explaining foreign policy decisions is to model the internal “world in their minds” in order to understand the “external world of events.” The empirical approach to measuring foreign policy decisions and their origins in the minds of decision makers is the microscopic content analysis of the event histories of observers and the belief inventories of leaders.