This chapter contains a brief overview and introduction to the field of personality psychology. Personality is defined as "the set of psychological traits and mechanisms within the individual that are organized and relatively enduring, and that influence his or her interactions with, and adaptations to, the environment (including the intrapsychic, physical, and social environment)." Each aspect of this definition is examined in detail, and the three key levels of analysis in personality psychology are introduced: 1) human nature; 2) individual and group differences; and 3) individual uniqueness.

Next, the authors discuss a long-standing fissure in the field of personality psychology, between the human nature level of analysis, and the analysis of individual and group differences. The authors suggest that focusing on several domains of personality knowledge can bridge this fissure. These six domains of knowledge are 1) the dispositional domain; 2) the biological domain; 3) the intrapsychic domain; 4) the cognitive-experiential domain; 5) the social and cultural domain; 6) and the adjustment domain. Each of these domains is discussed in turn.

The chapter ends with a discussion of the key features of a scientific theory and address how scientific theories differ from unsubstantiated beliefs, such as the belief in astrology.