This paper reviews principal effectiveness research and suggests measures that might promote effective principalship. The first section discusses principals' behavior patterns and conditions bearing on their effectiveness. Topics examined include role ambiguity, goal setting behavior, leadership and initiative, management behaviors, instructional management, symbolic leadership, personal characteristics, leadership styles, and situational influences. The second section proposes that states and school districts facilitate principals effectiveness by (1) giving principals a greater role in educational improvement programs; (2) selecting principals according to precise and explicit competencies while recognizing the symbolic importance of selection, using behavioral measures derived from such programs as internships and assessment centers, and matching principals to schools; (3) providing more relevant preservice and inservice training; and (4) improving school districts' organization and management by articulating districtwide goals while preserving school autonomy, and by developing comprehensive evaluation systems. Incentive programs are proposed as one means of supporting effective principals. (MCG)