Research over the past 50 years has yielded many promising early intervention approaches and techniques designed to enhance young children’s development. Yet virtually no systematic research has been conducted on the effects of different treatment intensities. In this presentation I will review how intervention intensity has been defined in both the research literature and in practice and propose a set of concepts and terms intended to capture the dynamic aspects of treatment intensity as a construct. On the basis of this approach, I will then discuss four types of knowledge that can be generated by treatment intensity studies, critical methodological and research design issues, and common issues faced by researchers and practitioners in clinical, education, and family settings.