In this article, I examine changes in the field of cognitive development and in my own thinking over the past 40 years. The review focuses on three periods. In the first, Piaget's theory was dominant, and my research and that of many others was aimed at understanding the many fascinating changes in children's thinking that Piaget documented, and correcting inaccuracies in his theory. In the second period, which involved efforts to formulate alternatives to Piaget's approach, I generated overlapping waves theory, and attempted to specify through microgenetic methods and computer simulations how development can be produced by variability of strategy use, adaptive choices among strategies, and discovery of new strategies. In the third period, my thinking and research, and that of many others, has focused increasingly on the interface between cognitive development and education. I close by suggest that generating domain-specific integrated theories of cognitive development may provide a way forward for the field.