Leadership theories attempt to explain the role leaders play in influencing others and the relationship between leadership and organizational effectiveness. Studies of leadership have been approached in a variety of ways with the ultimate goal of identifying variables that impact leadership and affect organizational performance. Historically, research has tended to focus on one aspect of leadership and a limited number of variables, and the resulting leadership theories are often categorized according to the researcher’s focus. In this chapter, leadership theories are classified into four categories: (a) trait theories of leadership, (b) power approaches to leadership, (c) behaviors of leaders, and (d) transformational, visionary, and moral leadership. Contemporary research on leadership provides more robust theories that frame leadership behaviors within various contexts and demonstrate a number of ways leaders influence organizational processes and systems. This chapter introduces the notion of leadership viewed from the lens of critical theory and explores integrated theories, such as flexible leadership and distributed leadership.