Daryl Siedentop has been viewed as one of the most influential scholars in the fields of physical education and physical education teacher education. In this article, we examine his epistemological lens, behavior analysis that he used to underpin his research and practice. After an introduction to behavior analysis, we discuss his approach to conducting research, and then we discuss some of his more significant contributions to the fields, providing attention to backstories of his work, what the work was, and how it impacted the fields of physical education and teacher education. Throughout, we use examples to highlight his contributions to the two fields.