The goal of this chapter is to summarize current knowledge about the development of individual differences in temperament and personality from childhood through adulthood. The chapter is divided into seven sections. The first two sections describe the most salient temperament and personality traits across the lifespan and offer a process-focused analysis of those traits, including their early antecedents and psychological and biological underpinnings. The third and fourth sections explore how early-emerging temperamental differences become elaborated into personality differences and summarize research evidence about the genetic and environmental origins of these differences. The fifth and sixth sections review new and accumulating evidence about continuities in personality development from childhood to adulthood and the influence of personality on life outcomes. The seventh section explores the connections between temperament and personality traits and psychopathology.