The purpose of this qualitative study was to determine how docents developed expertise within the context of their work with history museums. Twelve expert docents from four history-themed museums were interviewed to discover how expertise is developed by volunteers working in nonformal settings. Interpretation of the data revealed two primary means of preparation. First, formal training and continuing education were initially used by docents for learning their craft; and second, informal and incidental learning were critical to expertise development in museum docents. Based on the findings that emerged, implications for museum education and volunteer practice and the wider field of adult education are presented. (Contains 2 tables.)