Flavins are arguably one of the most versatile cofactors by virtue of the reactivity of the isoalloxazine ring system. A varied catalogue of reactions for the diverse family of flavoenzymes has been reported, leading to unifying concepts in (long-range) electron transfer, oxygen activation, photochemistry and substrate redox reactions. Recent examples of unprecedented flavin chemistry have been reported that uncover hidden depths of the flavoenzyme chemical repertoire. These include ring expansion of flavin through prenylation and formation of the superoxidized flavin-N5 oxide species. These and other new flavin based species are reviewed here and suggest further exciting discoveries await the flavoenzymology field.