Pioneering researchers in the role of temperament in personality development, Drs. Chess and Thomas helped to reverse the once dominant view that children’s behavioral differences can be explained solely by variations in environments.  In previous works, they elucidated their now widely accepted ideas about the various categories of temperament, including the three special types – the easy child, the difficult child, and the slow-to-warm-up child – and traced the role of temperament in normal and pathological personality development. Here, the renowned architects of the New York Longitudinal Study apply their insights to the clinical domain, offering concrete guidance to medical and mental health professionals and educators on how to identify temperamental characteristics and use that information to help “difficult” children and adults cope more successfully with the myriad and changing demands that their environments pose.