Developments in the assessment of general and maladaptive personality traits in children and adolescents have been reviewed in the present paper, with an emphasis on instruments based on the Five-Factor Model (FFM), such as the Hierarchical Personality Inventory for Children (HiPIC; Mervielde & De Fruyt, 1999), which describes general traits, and the Dimensional Personality Symptom Item Pool (DIPSI; De Clercq, De Fruyt, Van Leeuwen, & Mervielde, 2006), which accounts for maladaptive traits. We have additionally discussed measures available in Japanese, to assess traits in children, adolescents, and adults, and pertaining issues in cross-cultural personality research, especially with respect to Western and Asian differences. Finally, a number of key implementation areas for personality assessment have been identified, together with some challenges for this promising field of research.