The development of effective leaders and leadership behavior is a prominent concern in organizations of all types. We review the theoretical and empirical literature on leader and leadership development published over the past 25years, primarily focusing on research published in The Leadership Quarterly. Compared to the relatively long history of leadership research and theory, the systematic study of leadership development (broadly defined to also include leader development) has a moderately short history. We examine intrapersonal and interpersonal issues related to the phenomena that develop during the pursuit of effective leadership, describe how development emerges with an emphasis on multi-source or 360-degree feedback processes, review longitudinal studies of leadership development, and investigate methodological and analytical issues in leader and leadership development research. Future research directions to motivate and guide the study of leader and leadership development are also discussed.