Ziegler–Natta catalysis denotes coordination polymerization of olefins mediated classically by an early transition-metal compound, especially a titanium halide, together with an organoaluminum cocatalyst; supported MgCl₂-based formulations are prominent heterogeneous members of this catalyst family. The catalytic sequence comprises formation of a metal–alkyl active site, olefin coordination, and migratory insertion into the metal–carbon bond, which extends the growing chain and recreates a coordination site for another monomer ^[1]. In α-olefin polymerization, the local environment of the active center and the conformation of the chain end govern monomer-face selection and therefore polymer tacticity ^[2]. Heterogeneous multicomponent catalysts contain distributions of active sites, whereas soluble single-site catalysts express the same coordination–insertion logic in a molecularly defined ligand environment. The defining boundary is catalytic olefin chain growth by repeated coordination and insertion at a metal center; free-radical polymerization, cationic polymerization, and other pathways lacking metal-mediated insertion are not Ziegler–Natta catalysis.