The goal of this paper is to contribute to the revival of Heinz Werner's organismic-developmental theory by considering some of its key claims in relation to contemporary developmental theory and research. The organismic-developmental definition of development in terms of differentiation and integration is first discussed in relation to contemporary systems theory. It is then synthesized with contemporary sociocultural theory, specifically the position that development occurs as individuals participate with others in cultural practices. Ultimately, it is argued that defining development in terms of differentiation and integration offers a systematic framework for distinguishing between change and development. Some implications of organismic-developmental theory for conducting research are discussed, and the paper ends with suggestions for future theorizing and research.