Summary: In not more than 450 words the entry reviews the short history of the subject in political science, distinguishes between horizontal and vertical clientelism, and challenges the existing research to become more theoretical. In the 1950s political clientele structures first were analyzed in the form of political machine structures. Later this perspective was applied to other bossism issues in industrial and developing countries. The entry characterizes the object of study as the material and favor exchange relations between political actors, which often are illegal. While both parties gain, the power structure often leaves one side more dependent on the other. The entry distinguishes between horizontal or vertical forms of clientelism, depending on the position of the actors involved. Following a review of main empirical contributions to the study of clientelism, the entry suggest more typological work for the future to allow comparative analysis.