Rost (1993) discovered 221 different definitions and conceptions of leadership. The question of the correct definition of leadership is a nontrivial matter. Before discussing leadership, it is useful to define the term. This conception of leadership, known as the great man theory, evolved into the study of leadership traits, only to be supplanted later the theories under discussion here (Glynn & DeJordy, 2010). The idea is that leadership is a characteristic ability of extraordinary individuals. One of the earliest studies of leadership, Galton's (1869) Hereditary Genius emphasized a basic concept that informed popular ideas about leadership (Zaccaro, 2007). First, a brief history of leadership follows. The manuscript also discusses modern leadership challenges and leadership development in the context of all three theories. It presents a comparison and contrast of the key principles of each. It begins with introductory comments about the academic field of leadership, continues with a look at the three theories including their history and development, and proceeds to a micro-level, examining several recent published studies in each area. This manuscript analyzes three seminal leadership theories: situational leadership, transformational leadership (TL), and transactional leadership. Keywords: Leadership, Situational Leadership, Transactional Leadership, Transformational Leadership, Development, Review The manuscript also discusses the concept of leadership development in light of those three seminal theories and offers suggestions for moving forward both the academic study of leadership and the practical application of research findings on the field. Analysis of a sampling of recent articles in each theory is included. This manuscript describes three seminal leadership theories and their development. McCleskey (2014) argued that the study of leadership spans more than 100 years. In order to advance our knowledge of leadership, it is necessary to understand where the study of leadership has been.