Past work on interpersonal assertiveness and organizational effectiveness paints a mixed picture: some research suggests a positive link, other work highlights negative effects. This article reviews recent research and an account that stems from a different perspective, looking at assertiveness as a factor in leadership shortcomings and failure. This approach suggests that interpersonal assertiveness is a major factor and has a curvilinear, inverted-U-shaped relationship with leadership effectiveness. I review evidence for this effect as well as social and instrumental outcome mediators. I consider moderators and boundaries, sources of individual differences in assertive behavior, prospects for changing assertiveness, and factors in the perception of assertive behavior. Beyond the specific results I review, I argue that this program of work offers value by highlighting the lens of conflict as a generative perspective on leadership. Exploring how, and how hard, leaders fight pulls in insights from a variety of literatures and prompts new research that can help expand the scholarly portrait of leadership.