First published in 1986. This book is based on two simple ideas. The first is that genes are involved in change as well as continuity in development. The second is that the best way to study effects of environment on behavior is through the study of genetic influences, employing the theory and methods of quantitative genetics. These are the major themes of a new interdiscipline, developmental behavioral genetics, which applies the tools of quantitative genetics to the study of behavioral development. Research in developmental behavioral genetics has just begun, nonetheless significant advances already have been made and these have important implications for developmental psychologists.