Design principles are created to codify and formalize design knowledge so that innovative, archival practices may be communicated and used to advance design science and solve future design problems, especially the pinnacle, wicked, and grand-challenge problems that face the world and cross-cutting markets. Principles are part of a family of knowledge explication, which also include guidelines, heuristics, rules of thumb, and strategic constructs. Definitions of a range of explications are explored from a number of seminal papers. Based on this analysis, the authors pose formalized definitions for the three most prevalent terms in the literature—principles, guidelines, and heuristics—and draw more definitive distinctions between the terms. Current research methods and practices with design principles are categorized and characterized. We further explore research methodologies, validation approaches, semantic principle composition through computational analysis, and a proposed formal approach to articulating principles. In analyzing the methodology for discovering, deriving, formulating, and validating design principles, the goal is to understand and advance the theoretical basis of design, the foundations of new tools and techniques, and the complex systems of the future. Suggestions for the future of design principles research methodology for added rigor and repeatability are proposed.