Electrochemical polymerization is the formation of a polymer by oxidation or reduction of a monomer at an electrode, so that the chain-forming event is driven by interfacial electron transfer rather than by a chemical initiator ^[1][2]. In the chemistry of conducting polymers the concept is bounded by anodic or cathodic generation of a radical-ion or related intermediate from a polymerizable monomer—commonly aniline, pyrrole, thiophene, or a related aromatic—and by subsequent coupling that builds a conjugated or otherwise electroactive film on the electrode ^[2][3]. Essential features are a potential (or current) that sets the monomer’s redox state, an electrolyte that supports ion transport, and deposition of the growing polymer at the electrode surface, which couples film thickness to the passed charge. Online mass-spectrometric observation of aniline oxidation products confirms that the early intermediates are the expected coupling oligomers of the electrogenerated radical cations ^[3]. Templated electrochemical polymerization can transfer the morphology of a preorganized assembly into the growing conjugated chain ^[4]. The process is distinguished from chemically oxidative polymerization by the electrode as the oxidant (or reductant) and from electrophoretic deposition of a preformed polymer by the fact that the macromolecule is created in situ. Conceptual limits exclude electropolymerizations in which the current only heats the medium and does not oxidize or reduce the monomer.