Flavin catalysis has been developed as an environmentally benign route to novel redox chemistry, and the utility of these catalytic systems as simple models of flavoenzyme mechanism has been discussed. A system for oxidising aldehydes to carboxylic acids under flavin catalysis using a Bayer-Villiger type mechanism has been developed, which shows similarities to the enzyme bacterial luciferase. An oxidation of primary amines, using alloxan as co-catalyst and a sulfide as reducing agent, was developed. This was found to work efficiently using air as terminal oxidant, and by extensive mechanistic studies involving EPR spectroscopy, kinetics and UV/visible spectroscopy we propose a radical mechanism. The similarities in some kinetic properties of our system to monoamine oxidase (B isozyme) led us to re-evaluate some previously published pKa dependence data. The catalytic activity of alloxan itself was evaluated, in conjunction with a Cu(I) co-catalyst, and was found to be effective in oxidation of amines, including oxidative cross-coupling, as well as for diimide-like reductions of alkenes and alkynes with hydrazine. Finally, flavin-indole charge transfer chemistry was found to promote selective C3-deuteration of indoles. The CT complex was isolated and found to form a flavin-indole covalent bond under certain conditions. Additionally, we found that in situ DCl generation was a viable method for indole deuteration with very short reaction time and high selectivity compared to previous methods.