This book examines the role of ideologies and belief systems in individual decision-making behavior from an economic and rational perspective. Due to the fact that people have incomplete information, belief systems and ideologies fulfill a number of important functions. While ideologies themselves serve psychological needs, they are used as a cognitive framework for rational decision-making once they have been adopted through a Bayesian learning process. They influence decisions in a wide range of areas, from consumption and work to politics. This is where the role of ideological organizations becomes important, because they determine the ideological direction of the narratives and their dissemination.