This special issue of the "Courrier," a journal for professionals concerned with issues related to the physical and psychological development of children, provides (1) an overview of 25 years of internationally coordinated research, (2) a selection of papers published by the research teams, and (3) a description of the teams and their present status. The origin and international expansion of the program for longitudinal studies is described in the first article. The subsequent 15 articles cover a wide range of topics. Studies concerned with physical development focus on the skeletal maturation of the hand and wrist; growth in the density of normal infants' subcutaneous cellular tissue; age of onset of menarche and associated factors among Parisian girls; clinical transformations of puberty in young girls; international comparisons of infants' physical growth; development and maturation of young children in Dakar; Gessell tests on African children; parent-child correlations for body measurements of children between the ages of 1 month and 7 years; the somatic development of urban, Swedish children; and analysis of the adolescent growth spurt using smoothing spline functions. The one study focused solely on psychological development discusses intellectual development from birth to 18 years of age. Studies covering both psychological and physiological development examine bowel and bladder control during the day and at night in the first 6 years of life; trends in the development of abilities related to somatic growth; individual differences as seen in developmental and intelligence quotient curves from 6 months to 17 years; and a comparison of infant development in five western countries. (Author/RH)