This chapter explores the leadership theories in organization studies and their link to executive coaching. It starts by examining the various attempts to define ‘leadership’ and then provides an overview for each of eighteen different categories of theories and research on leadership. These are: trait approach; skills approach; style approach; situational approach; contingency theory; path—goal theory; leader—member exchange theory; transformational leadership; servant leadership; authentic leadership; team leadership; psychodynamic approach; women and leadership; culture and leadership; leadership ethics; spiritual leadership; adaptive leadership; and the complexity theory and social constructionist approaches to leadership. The chapter concludes with reflections on the current developments in leadership theorizing and how the executive coaching field can benefit from them.