Stella Chess's scientific contributions are of major importance. The New York Longitudinal Study, started in 1956 and still going strong, is her tour de force. Chess not only recognized in a detailed and carefully observed way that children had individual styles of behavior, she also discovered a clinical method of interviewing the parents that provided accurate descriptions of these special characteristics of the child. The scientific research problem of organizing the data was solved by Herbert Birch and his co-worker Margaret Hertzig, who together identified nine separate qualities, or traits, that constituted what came to be called the temperament of the child. Birch also developed the quantitative rating system used for each temperament trait. Chess discovered three broad categories of temperament—"the easy child," "the difficult child," and "the slow-to-warm-up child." The first publication appeared in 1957 (1). More articles quickly followed, and in 1960 the true heart of the matter was revealed in an important paper by Chess, Thomas, Birch, and Hertzig called "Implications of a Longitudinal Study of Child Development for Child Psychiatry" (2). The concepts and the research were quickly picked up in many parts of the world, including England, where Michael Rutter in 1963 first used the term "temperament" and considered its genetic aspects.