Discusses the 5-factor model as a comprehensive model of personality traits (Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness). The claim that these 5 factors represent basic dimensions of personality is based on 4 lines of reasoning and evidence: (1) longitudinal and cross-observer studies demonstrate that all 5 factors are enduring dispositions that are manifest in patterns of behavior; (2) traits related to each of the factors are found in a variety of personality systems and in the natural language of trait description; (3) the factors are found in different age, sex, race, and language groups, although they may be somewhat differently expressed in different cultures; and (4) evidence of heritability suggests that all have some biological basis. To clarify some remaining confusions about the 5-factor model, the relation between Openness and IQ is described, and problems in factor rotation are discussed.