Only 0.016 % of all known natural products contain an aziridine ring, but this unique structural feature imparts high reactivity and cytotoxicity to the compounds in which it is found. Until 2021, no naturally occurring aziridine-forming enzymes had been identified. Since 2021, the biosynthetic enzymes for ~10 % of known aziridine containing natural products have been identified and characterized. This article describes the recent advances in our understanding of enzyme-catalyzed aziridine formation in the context of historical methods for aziridine formation through synthetic chemistry.