Trait theory is an approach to personality theory in psychology.

According to trait theory, personality can be broken down into a limited number of traits, which are present in each individual to a greater or lesser degree. This approach is highly compatible with the quantitative psychometric approach to personality testing, especially the use of factor analysis to summarise the results of such tests. The factors are readily conceptualised as measurements of traits. Correspondingly, trait theory has come under attack from those who preferred a more qualitiative, intuitive approach to personality analysis, and psychometrically inclined personality theorists are often accused of reifying as traits measurements that are simply mathematical abstractions.

In general personality theory, the traits discussed tend to be broad tendencies such as extraversion or neuroticism. Within specific fields or applications of psychology, more specific traits have been discussed. For example, there was an early trait theory of leadership that went through several conceptual stages through different researchers. Eventually, six traits were distinguished that were correlated with strong leadership ability: