The 15^th International Symposium on Biocatalysis and Biotransformations (Biotrans 2021) will be hosted as an online conference by the University of Graz, Austria. The Biotrans 2021 symposium provides the unique chance to bring the recent advances in biocatalysis research to every location in the world. An exciting program has been set up covering new reactions, design of enzymes, understanding enzyme mechanisms, applications, computational methods, (chemo)enzymatic cascades and chemo-inspired reactions. To allow a lively exchange between all participants, special emphasis has been put on interactive poster sessions as well as networking events.