Polymer chemistry textbooks (e.g., B. Vollmert, Polymer Chemistry, Springer-Verlag: New York, 1973, p 37; G. Odian, Principles of Polymerization, 3rd ed., Wiley: New York, 1991, p 8; H. G. Elias, An Introduction to Polymer Science, VCH: Weinheim, 1997, p 51) classify polymerization reactions as chain, step, and living according to the dependence of their degree of polymerization (<(DP)over bar>) or molecular weight ((M) over bar) on conversion. This article discusses the rationale for uniform terminology in living polymerization.