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A stereochemical polymerization in which an achiral monomer is converted into a one-handed helical polymer under the influence of a chiral catalyst, initiator, or medium is helix-sense-selective polymerization. The newly formed macromolecule is optically active because of a preferred screw sense (P or M), not because the monomer itself is chiral. Chiral rhodium catalysts polymerize achiral phenylacetylenes bearing hydroxy groups to helical polyacetylenes of preferred screw sense ^[1]. Air-stable palladium initiators effect living and helix-sense-selective polymerization of diazoacetates, linking molecular-weight control to helical induction ^[2]. Helix-sense-selective polymerization of carbodiimides and of guanidine monomers likewise produces permanently optically active helical chains when the chiral initiator sets the screw sense at the chain end ^[3]. The concept is a subset of asymmetric polymerization restricted to helical chirality. Polymerization of an enantiopure chiral monomer that merely inherits point chirality is not helix-sense selective unless a helical bias is additionally imposed. Racemic pairs of helices from achiral initiators lie outside the term.