Efforts to reform and improve teaching and learning in the undergraduate science, technology, engineering, and mathematics (STEM) disciplines have grown increasingly stronger and more focused over the past two decades. Since the early 1990s, some notable unifying developments have given coherence to such initiatives, as well as other developments that have contributed to their disciplinary depth and embeddedness. In this chapter, the authors provide some historical perspective on the ways in which these reform efforts have evolved. National organizations and entities, including the National Research Council (NRC), National Science Foundation (NSF), Project Kaleidoscope (PKAL), accrediting agencies, and coalitions of institutions of higher education, as well as efforts in which disciplinary professional societies have been deeply involved, have had significant influence. The authors also provide examples of discipline-based efforts to improve and enhance STEM education drawn from the past two decades. These examples were chosen to emphasize the range of geneses, approaches, and impacts in undergraduate reform.