“Leader credibility” is believed by many scholars as essential for effective leadership and is commonly used in discussions about leaders in business, politics, and other areas. Yet despite leader credibility’s strong presence in contemporary press and research, the “leader credibility” construct is not clearly conceptualized, and a grounded understanding of leader credibility is missing. To begin building a solid foundation of leader credibility knowledge, we conducted a systematic literature review (SLR), which included 108 peer-reviewed articles representing various disciplines. This paper presents our descriptive and content-based findings. Our results reveal a significant research gap: despite the breadth and depth of the research on leader credibility, leader credibility is not consistently defined or measured. We provide an accounting of knowledge to date and illustrate this concept’s weak footing. Finally, we outline an array of relevant research paths that are possible after scholars reconceptualize the leader credibility foundation.