The central thesis of this paper is that grand theories of development are alive and well and should be paramount to those interested in behavioral intervention. Why? Because how we think about development affects how we approach treatment. Here I discuss the central concepts of a new theory of development—dynamic systems theory—to highlight the way in which a theory can dramatically alter views of what intervention is all about. Rather than focusing on one root of maladaptive behavior such as biological predispositions, environmental causes, or motivational states, dynamic systems theory presents a flexible, time-dependent, and emergent view of behavioral change. I illustrate this new view with a case study on how infants develop the motivation to reach for objects. This example highlights the complex day-by-day and week-by-week emergence of new skills. Although such complexity presents daunting challenges for intervention, it also offers hope by emphasizing that there are multiple pathways toward change.