This review systematically describes the synthesis and reactions of epoxides and aziridines using organocatalysis, and includes their reactions like desymmetrization, regioselective nucleophilic ring-opening and cycloaddition with CO₂. Based on the various generic modes of activation of organocatalysis, a systematic classification of organocatalysts used for regioselective nucleophilic ring-opening of epoxides and aziridines is given.