Polyamide synthesis constructs macromolecules in which amide groups, –C(=O)–NH–, are recurring main-chain linkages. Two principal routes define the class: step-growth polycondensation of diamines with dicarboxylic acids or activated derivatives, and ring-opening polymerization of lactams ^[1][2]. AA/BB monomer pairs require near-equimolar functional groups and high conversion to reach high molar mass, whereas AB amino acids contain both functions in one monomer. Lactam polymerization is a chain process initiated by water, acids, bases, or activated lactam species; anionic ring-opening is especially important for nylon formation ^[2]. Aliphatic nylons and aromatic aramids both satisfy the definition because the amide linkage belongs to the backbone, although their monomer structures and polymerization conditions differ. Polyamide synthesis is distinguished from peptide synthesis by its synthetic-polymer context and from polyester, polyurethane, and polyimide synthesis by the identity of the repeat linkage. Polymers bearing only pendant amides are not polyamides under this constitutional definition.