The report summarizes a literature search conducted in the areas of individual differences, task characteristics, organizational structure, and external environment as they relate to leader behavior. The studies reviewed supported the notion that effective leader behavior was conditioned by complex relationships between personal variables and situational variables such as task characteristics. Problems in defining task variables were noted and classification schemes were reviewed providing suggested dimensions along which tasks vary. Research showed that task variables were important for determining effective leadership style. Definitions, problems, and properties of group and organizational structure were reviewed. Finally recent efforts to develop theory and data relating change in the external environment of organizations to leader behavior were summarized.