The mechanism of coating formation by electropolymerization of poly(2-vinylpyridine) has been studied on a copper electrode by surface-enhanced Raman scattering spectroscopy and cyclic voltammetry. The experimental results are consistent with a mechanism in which 2-vinylpyridine molecules become protonated in acidic aqueous solutions and are selectively adsorbed on cathodic surfaces. The adsorbed 2-vinylpyridinium ions then undergo electrochemical reduction to free radicals, which initiate polymerization by combining with neutral 2-vinylpyridine molecules also present in solution. The pH of the electrolyte has been found to be critical for this process. On the basis of the voltammetric experiments, an additional mechanism for polymer growth on the cathodic surface at more negative potentials is proposed. This involves protonation of nitrogen sites along the newly formed poly(2-vinylpyridine) chains, followed by their reduction to form polymeric radicals that can initiate chain branching. In this way, inactive polymer chains can be reactivated and highly branched and cross-linked poly(2-vinylpyridine) coatings can be formed, leading to the relatively low solubility of these coatings in typical organic solvents.