This chapter discusses a core problem that has plagued the study of intelligence for decades, the complexity of behavior. The central tenets of dynamic systems, which underpin efforts to analyze the organization and development of behavior in its complexity are outlined, keeping person and context connected and treating variability as the starting point for analysis. The classic approaches to intelligence, psychometric, Piagetian, nativist, and dynamic/constructivist are reviewed. The chapter explains how disputes between them have illuminated learning sequences, resolved important questions, and paved the way for a dynamic approach to intelligence are shown. The dynamic skill theory framework, emphasizing its conceptual origins in dynamic systems, ways that it has advanced understanding variability and consistency in intelligence, and its relevance to understanding childhood intelligence are introduced. The areas where dynamic systems concepts and models have generated usable knowledge directly relevant to intelligence, learning, and the practice of education are considered.