The article emphasizes the importance of theory construction for comparative policy research. Attempts to identify the impact of institutional arrangements on policy choices are complicated by interaction effects between institutionalized boundary and decision rules on the one hand, and `decision styles' on the other hand - which are defined as cognitive and normative patterns that characterize the way in which interests are defined and issues framed and resolved under the applicable rules. A typology of such styles is developed with reference to recent findings of experimental social psychology, and the empirical implications of different combinations of decision rules and decision styles are examined in a game-theoretical context.