One of the more fruitful systematic approaches to the study of foreign policy views nations as information processors and explains foreign policy as a function of information and processing thereon. Much of such processing depends on the prior beliefs of decision makers, but for a variety of reasons these systems of prior beliefs are very difficult to analyze using “standard” empirical and modeling techniques. Computational modeling, including expert system technology, provides an alternative methodology that allows such analysis. I present Policy Arguer (POLI), an expert system model of U.S. foreign policy making in Asia. Poli has been very successful in reproducing actual U.S. responses to events in Asia from the 1950s. More important, POLI recreates policy debate in the form of the arguments and counterarguments used to justify policy alternatives. The model explains foreign policy outputs in terms of a complete process from foreign policy beliefs, through debate, to choice.