A detailed analysis of elementary reactions of carbocationic polymerization culminated in the prediction and subsequent experimental demonstration of quasiliving polymerization. Quasiliving polymers are formed in a system provided that the process of chain termination and chain transfer to monomer are absent or reversible, i.e., the propagating ability of the chain end is maintained throughout the experiment, and the molecular weight increases in proportion to the cumulative amount of monomer added. The chain end can be active (carbocation) or dormant (reactivable polymeric olefin or cation source). Chain transfer is suppressed by keeping the monomer concentration low. Quasiliving polymerizations are maintained by continuous slow feeding of dilute monomer to a charge containing the initiating or propagating species (quasiliving polymerization technique). A comprehensive kinetic scheme has been developed that describes quasiliving polymerization in quantitative terms. Quasiliving polymerization was demonstrated experimentally in the “H2O”/BCl3/α-methylstyrene and cumyl chloride/BCl3/α-methylstyrene systems.Mnversus monomer input plots are linear over wide ranges, indicating quasiliving conditions, and poly(α-methylstyrenes) withMn> 2 × 105have been obtained, Molecular weight distributions were found progressively to narrow and dispersion ratiosMw/Mnto decrease.