The focal objective of this thesis was to examine the potential advantage of introducing the self-schema concept, indexed by response time, into personality assessment. The basic rationale for the use of response time is that a self-schema facilitates response time for self-referent information as it permits people to make assessments easier and automatic. A self-schema is a cognitive structure containing the generic knowledge that people have about themselves, influencing all aspects of the processing of self-relevant information in order to organize, summarize and explain their behavior. Paper I examined the self-schema proposition that the relation between personality score and response time for the Big Five personality factors is curvilinear in accordance with the inverted-U effect. Using more appropriate statistical methods than in previous studies, Study 1 and Study 2 confirmed the existence of the inverted-U effect for all Big Five factors. Thus the results provided support for the self-schema perspective as people scoring low or high on the Big Five traits responded faster than those scoring in the middle. Previous research has shown that the Big Five personality factors Openness to Experience and Agreeableness are powerful predictors of prejudice. The main question in Paper II was whether this prediction could be improved by including a measure of self-schema (schematicity). The results of Study 3 demonstrated that response time significantly improved the prediction of generalized prejudice from the mentioned personality factors and disclosed both an additive and a moderating effect. Thus, the relation between personality trait score and generalized prejudice is moderated by how schematic a person is. Paper III examined the potential linkage between heritability and self-schema. In Study 4, 5, and 6, the relation between heritability and response time for the Big Five personality facets (subfactors) was examined. The results revealed that personality response time is related to personality heritability so that shorter response times are associated with higher heritabilities. Putting the present results into the context of self-schemas, this means that Big Five personality facets with a large heritability on the average would have higher schematicity than those with small heritability estimates. The results of the present thesis extend previous work in the area of self-schema. The findings suggest that self-schema, measured by response time, may be a useful additional tool to fine-tune personality assessment. Also, the findings put emphasis on the importance of considering possible curvilinear relationships and interaction effects in order to better comprehend the rationale underlying self-schemata processing.  Finally, the results imply that the heritability of personality traits should be taken into account when we construct theories and models in personality psychology. The implications of these results are discussed and directions for future research are highlighted.