In this chapter, students will investigate the diverse factors that shape an individual's personality, including traits, temperament, and the influence of both genetic and environmental factors. They will explore the major theoretical perspectives on personality, such as the psychoanalytic, trait, and social-cognitive approaches, and how these frameworks contribute to our understanding of individual differences in behavior, cognition, and emotional expression. The chapter will also delve into the assessment and measurement of personality, and its applications in various domains, including clinical psychology and organizational settings.