The Index of Independence in Activities of Daily Living (Index of ADL) is a scale whose grades reflect profiles of behavioral levels of six sociobiological functions, namely, bathing, dressing, toileting, transfer, continence, and feeding. Its hierarchical nature makes it possible to rank the overall functional status of people in an ordered manner, to make comparisons among them as individuals or groups, and to detect changes over time. Developmental studies have encompassed children as well as adults, the mentally retarded as well as physically disabled, and noninstitutionalized as well as institutionalized people. In view of relationships to behavior of primitive societies and parallelisms between the order of index functions and patterns of child growth and development, the Index of ADL appears to be based on functions of sociobiological primacy. This concept is supported by twenty years of methodological and applied observations. The Index has been used to produce predictive information about chronic conditions and to evaluate the benefits of long-term services. It has been used in profiled measures of severity of illness. As a screening measure and survey measure, it has contributed information about health needs and outcomes which is useful for management, planning, policy making, research, and techning.