Child psychologists and psychiatrists are interested in assessing children's personalities. This interest is fueled by the practical desire to identify differences between children that have predictive utility, and by recognition that future advances in developmental theory, especially in relation to gene-environment interplay, can only be as good as the measures on which they rely. The aim of this article is to facilitate these practical and theoretical advances. First, we delineate a taxonomy of measurable individual differences in temperament and personality in childhood, and point the reader to proven and/or promising measuring instruments. Second, we describe the processes through which early temperament differences may become elaborated into adult personality structure and lifelong adaptation, and identify gaps in the empirical research that need to be filled. Third, we explore the various connections between temperament/ personality traits and psychopathology, and direct attention to promising questions and strategies.