Based on the view that individual variability is best understood as the result of influences from multiple domains operating over time, this book describes how different domains of influence operate, describes the operating processes in common to the different influences, and shows how these processes meet the criteria for a full-fledged system. Chapter 1 illustrates the range of individual human behavioral-developmental variability and how the range observed is incompatible with explanatory models based on the operation of a single isolated developmental influence. Chapters 2 through 7 focus on influences on individual human behavioral-developmental variability and document how each influence, although necessary, is not sufficient when considered in isolation. Influence domains discussed are: evolutionary and ecological; genetic, neural, and hormonal; biomedical and nutritional; specific individual characteristics; proximal environment; and the distal environment. Chapter 8 focuses on various functional and structural linkages among developmental influences from various domains. Chapter 9 deals with the operation of these influences over time and how such influences tend to be specific rather than general in their impact. Chapter 10 documents how the operation of multiple developmental influences and midlevel processes meet the criteria for a system and how principles derived from dynamic and general systems theories form an additional level of influences on individual behavioral-developmental variability. It is proposed that individuals begin to operate in a manner akin to a general system. Chapter 11 shows how principles derived from the impact of multiple developmental influences and midlevel and systems processes can be applied to assessment of and intervention with children at risk for developmental problems. (Contains 1,161 references.) (KB)