In 1956 Stella Chess and Alexander Thomas launched the pioneering New York Longitudinal Study, a systematic investigation into the concept of temperament that has been pursued to the present decade. The findings from this study - that temperamental profiles of infants, children, adolescents, and adults show specific individual behavioral characteristics - are accepted as basic to the psychological mechanism of behavioral functioning. Now, these two preeminent authorities and teaches in the field of child and adolescent psychiatry present an essential introduction to their internationally recognized work. This volume takes the reader from concept - including the definition of temperament and the studies that support and expand upon that definition - to specific explorations of temperament and its impact across various practice settings and special populations.