Although the institutional contexts of prime ministers in parliamentary democracies and of U.S. presidents are very different, both types of executive leaders influence the decision-making processes through their leadership styles. Leadership style includes how the leaders relate to those around them, how they like to receive information, and how they make up their minds. While there are numerous empirical studies and theoretical frameworks on the leadership styles of U.S. presidents, few studies of prime ministers are concerned with personality and styles of leadership. This paper reviews the literature on U.S. presidential styles and on organizational leadership in order to construct a framework for the study of prime minister leadership styles. Components of the proposed framework are illustrated with examples of British prime ministers and German chancellors. In addition, categories of dependent variables to be explained by leadership style are discussed. I argue that leadership style has the greatest impact on the decision-making process and that although the direct effect of leadership style on foreign policy behavior is less, leadership style indirectly influences foreign policy through the decision-making process.