This chapter considers the juxtaposition of the basic principles of developmental theories and sweeping demographic changes. It discusses the broad concepts of normality, abnormality, and disability. The chapter discusses basic principles of developmental theories, including chronological age, social age, the continuity of development, control or agency, autonomy, epigenetic growth, cumulating advantages and cumulating disadvantages, and developmental tasks. It discusses the demographic changes such as the longevity revolution, the increasing diversity of the United States, the changing labor market, and the growing economic inequality. The chapter draws two broad conclusions: These demographic shifts occurred more rapidly, were more pervasive, and were of longer duration than expected. The chapter discusses the impact of these demographic changes on individuals with disabilities (IWDs).