This review identifies key issues associated with the design of future longitudinal studies of human development. Sixteen international studies were compared for initial response and retention rate, sample size, type of data collected, and sampling frames. The studies had little information about the influences of fathers, extended family members, childcare, and educational institutions; the effects of peers; children's use of time; the needs of disabled children; urban versus rural environments; or the influence of genetic factors. A contemporary longitudinal study should include measures of physical and mental health, cognitive capacity, educational attainment, social adjustment, conduct and behavior, resiliency, and risk-taking behaviors. It needs to address genetic and intergenerational factors, cultural identity, and the influences of neighborhood, community, and wider social and political environments and to encompass outcomes at all life stages to systematically determine the role each factor plays in individuals' lives, including interactions within and across variables.