Principals' behaviors and the reasons for and consequences of their behavior are the focuses of this review of major published empirical research on public school principals. Appended to the paper is a 70-page bibliography of doctoral dissertations, conference papers, and other writings on the principalship that were not reviewed. The author first discusses the different images of the principal that guide research and the various research methods used. After reviewing early principalship studies of the 1950's and 1960's, he examines the variables studied and not studied in the areas of principal characteristics, such as demographic and personality traits; principals' problems, including time use and relations with people and groups; and principals' perspectives or point of view, involving the problem- and management-oriented, face-to-face nature of the job. Ten neglected avenues for principalship research are identified, including school characteristics, private schools, managerial roles, external school environments, and job socialization. The paper's last sections suggest future research directions and discuss the literature's implications for principal training and selection. The appended bibliography of principalship research covers 10 topical areas, among which are multivariate studies and studies of principal effectiveness, characteristics, roles, and selection. (RW)