This paper explores the role of personality traits in predicting and causing academic and economic success, health, and criminal activity. It reviews evidence on the "situational specificity" of personality traits and preferences, examining whether personality psychology has relevance for economics. The paper discusses the biological and evolutionary origins of personality traits, the measurement systems used by psychologists, and the relationship between personality measures and cognitive measures. It compares the predictive power of personality measures with that of cognitive measures, finding that personality measures are equally predictive for many outcomes, even after controlling for family background and cognition. The paper also highlights the malleability of personality traits over the life cycle, suggesting that interventions to change personality traits could be promising avenues for addressing poverty and disadvantage. The authors use economic theory to formalize insights from personality psychology and develop models that explore causal mechanisms. They address questions such as how psychological constructs fit into economic frameworks, the relationship between economic preference parameters and psychological measurements, and the stability and malleability of personality traits and preferences. The paper concludes with provisional answers to these questions, emphasizing the importance of integrating personality psychology into economic research and policy analysis.This paper explores the role of personality traits in predicting and causing academic and economic success, health, and criminal activity. It reviews evidence on the "situational specificity" of personality traits and preferences, examining whether personality psychology has relevance for economics. The paper discusses the biological and evolutionary origins of personality traits, the measurement systems used by psychologists, and the relationship between personality measures and cognitive measures. It compares the predictive power of personality measures with that of cognitive measures, finding that personality measures are equally predictive for many outcomes, even after controlling for family background and cognition. The paper also highlights the malleability of personality traits over the life cycle, suggesting that interventions to change personality traits could be promising avenues for addressing poverty and disadvantage. The authors use economic theory to formalize insights from personality psychology and develop models that explore causal mechanisms. They address questions such as how psychological constructs fit into economic frameworks, the relationship between economic preference parameters and psychological measurements, and the stability and malleability of personality traits and preferences. The paper concludes with provisional answers to these questions, emphasizing the importance of integrating personality psychology into economic research and policy analysis.