The purpose of this study is to develop a set of competencies for public library directors, which can help them to successfully lead their libraries. The research objectives for this study were: to identify in the literature and report desired competencies for library manager/leaders drawn from the literature; to validate the competencies found in the literature through the opinions of current library manager/leaders; and, to refine the competencies found in the literature through the opinions of current public library directors. In this study to develop competencies for public library directors, a content analysis of the literature was done to find the important ideas in the literature. Then a Delphi method was used to refine that set from the literature to establish a final set of competencies important over the next decade. No one will develop perfect mastery of all nineteen competencies - or on all of any competency set. But the important thing is that standards are established to guide directors, to give them the best chance to be successful - for themselves and for their libraries. The final set of nineteen research-informed competencies should help them achieve professional success, and help their libraries to be as strong as possible in serving their communities.