In this article, I argue for a renewed focus in mathematics education research on procedural knowledge. I make three main points: (1) The development of students' procedural knowledge has not received a great deal of attention in recent research; (2) one possible explanation for this deficiency is that current characterizations of conceptual and procedural knowledge reflect limiting assumptions about how procedures are known; and (3) reconceptualizing procedural knowledge to remedy these assumptions would have important implications for both research and practice. (Contains 1 table.)