In this article, I provide the first publication thoroughly detailing how the theoretical foundation for the self-regulated strategy development (SRSD) instructional model was developed. I explain the development of the theoretical base for the SRSD model of instruction and the initial focus on writing instruction. I detail the reasoning and research that provided the base for the theory underlying the SRSD model of instruction. The theoretical base relies, in part, on both theoretical integration and triangulation; I define and provide examples of each process. I address the role of multiple theories, early studies, and iterations that led to the current SRSD instructional model. The tenets of the theoretical base, theoretical principle, and four initial and foundational research questions for the SRSD instructional model are detailed. Research regarding the four initial research questions is summarized, demonstrating the tenets and theoretical principle behind the SRSD model of instruction are valid and meaningful. A sizeable body of research across multiple countries indicates moderate to large effect sizes across many outcomes of SRSD instruction in writing and other complex learning areas. Finally, I address both directions for future research and significant challenges in scaling up SRSD instruction, including paradigm wars and other barriers.