When the focus for entry-level mathematics shifted, over a decade ago, from access to success, it catalyzed demand for accelerated multiple mathematics pathways alongside the algebraic-intensive pathway. Subsequent successes have been exciting, showing more than three times the success rates for students in one third of the time for some programs. With these startling increases came a widespread concern about maintaining rigor within the discipline. In response to this concern, the Charles A. Dana Center engaged in a study of the meaning and intention of rigor in mathematics education. This paper first explores the meaning of rigor in mathematics education through a synthesis of interviews with leading mathematicians and educators, and presents a review of the literature in higher education and K–12. It concludes by offering recommendations for a shared definition of rigor and its implications for curriculum and instruction.