The study of temperamental contributions to the development of the child has enjoyed a great deal of popularity over the last 20 years due, in part, to the writings of Thomas and Chess (1997). Most investigators regard the term temperament as referring to a number of moderately stable psychological profiles, under some genetic constraint, that emerge during infancy or early childhood. There is some debate, however, on the number of temperaments, how they should be measured, and whether they should be conceptualized as continua or as categories.