This chapter explores the applicability of the error-and-bias literature to world politics by examining experts' expectations for the future as well as their explanations of the past. One set of studies tracks the reactions of experts to the apparent confirmation or disconfirmation of conditional forecasts of real-world events in real time. Key issues become: (1) the extent to which experts who “get it wrong” resort to various belief-system defenses; (2) the effectiveness of these defenses in helping experts who got it wrong to preserve confidence in their prior world views; (3) the rationality of these defenses. The other set of studies examines retrospective reasoning: the tightness of the connection between experts' conceptions of what would have happened in “counterfactual worlds” and their general ideological outlook. The key issue becomes the extent to which counterfactual reasoning about historical possibilities is theory-driven (predictable from abstract preconceptions) as opposed to data-driven (constrained by the peculiar “fact situation” of each episode). In these studies of both prospective and retrospective reasoning, individual differences in cognitive style and in conceptual orientations are important moderator variables. Although there is a general tendency among our experts to rely on theorydriven modes of reasoning and to fall prey to theory-driven biases such as overconfidence and belief perseverance, these tendencies are systematically more pronounced among experts with strong preferences for parsimony and explanatory closure.