In this chapter, we review leadership research, with special attention to the questions that psychologists have addressed. Our presentation emphasizes that the phenomena of leadership can be predicted by a wide range of situational, social, and individual differences factors. Although not organized into a single, coherent theory, these bodies of knowledge are sufficiently related that we are able to piece together a moderately cohesive picture of leadership. This emergent understanding derives from research based on highly varied research methods, the most important of which we review and evaluate in this chapter.