The process of change represents a main, central issue for the study of development. Basic and applied researchers in developmental science have aimed their research work at answering several key questions related to the problem of change. How does change occur? What mechanisms produce change? What conditions are likely to promote the emergence of change in development? Another related question concerns the stability versus instability of new behavioral patterns that emerge as a consequence of an intervention. What are the relationships between variability and stability in developmental processes? Does the emergence of new behavioral patterns tend to suppress the old patterns or to coexist with them? Nevertheless, observing and understanding how change occurs has been recognized to be a quite difficult and challenging task (Miller & Coyle, 1999;Siegler & Crowley, 1991). This is despite recent advances in both theoretical perspectives and methods focused on change processes that have brought considerable progress in the research field (see "Microgenetic designs as promising tools," below). Part of the challenge is due to the complexity of conceptualizing change processes. It is our contention, however, that the main problem appears to come from the difficulty of devising and implementing appropriate methods for studying change while it is occurring (Fogel, 1990;Kuhn, 1995;Siegler, 1995), instead of comparing pre-and post-change behavioral patterns.In this chapter, we aim to illustrate a research design, referred to as microgenetic designs, specifically devised for documenting change processes in development. First, we discuss the limitations of traditional research designs to capture ongoing processes of change. We then present microgenetic designs through an illustration of their key characteristics. This is followed by a review of the theoretical foundations of microgenetic designs as well as some of the historical and current observational and experimental