This article describes oxidising enzymes used for biocatalytic applications. Redox biocatalysts are highly sought after because of the selectivity, controllability and economy of their reactions, in comparison with conventional chemical reactions. Increasing numbers of oxidative biotransformations are being reported, indicating wide variability in the biocatalyst characteristics and a range of potential and established applications. Several limitations apply to oxidative biotransformations, including the requirement for cofactor regeneration, and low stability and activities. Recent advances in addressing these problems include molecular and reaction engineering approaches.