Step-growth union of bifunctional or multifunctional monomers with extrusion of a small molecule (water, alcohol, hydrogen halide, or the like) is condensation polymerization. Each linking step is a condensation reaction, and molecular weight rises only at high conversion according to Flory’s statistical relation between extent of reaction and degree of polymerization ^[1]. Typical products are polyesters, polyamides, polyimides, and related heteroatom-rich backbones. Chain-growth condensation polymerization is a controlled variant in which substituent or catalyst effects suppress random step-growth and confine propagation to the polymer end, yielding well-defined condensation polymers and block copolymers ^[2]. The same principle enables precision synthesis of aromatic polyamides and π-conjugated polymers when catalyst-transfer or substituent-transfer activation keeps the chain end uniquely reactive ^[3]. The conceptual boundary versus addition polymerization is the stoichiometric byproduct and the step-growth (or chain-growth-condensation) kinetics. Not every step-growth polymerization is a condensation: polyurethane formation by isocyanate–alcohol addition is step-growth addition, not condensation, because no small molecule is eliminated.