Concepts without percepts are empty; percepts without concepts are blind. Immanuel Kant

The foregoing quotation reflects the view that theories and facts must evolve together in order for knowledge to develop. Textbooks in industrial-organizational (I-O) psychology and organizational behavior (I-O-OB) focus on specific research topics (e.g., motivation and leadership), and offer few conceptual connections between them. But a common theme underlies every topic-the theme is people (or human nature)—human nature underlies all discussions of people at work in organizations. Because personality theory concerns the nature of human nature, it provides a conceptual basis for understanding organizational behavior and occupational performance. This chapter is organized into three sections. The first section summarizes our perspective on personality. The second section outlines our perspective on personality measurement. In the third section, we review the literature regarding the links between personality and occupational performance, personnel selection, and leadership. We close with a discussion of a dreary but unavoidable topic-faking.