In 2004, unspecific peroxygenases (UPOs) from fungi were first identified and showed to catalyse selective oxygenation reactions, with high turnovers, good stability and a broad reaction scope, providing a valuable alternative to established biocatalytic hydroxylation systems such as cytochrome P450s. At the start of this project, access to UPOs was limited to expression in their native fungi, hence studies were performed looking into heterologous expression of the enzymes from Agrocybe aegerita and Agaricus bisporus, followed by characterisation, and application of the enzymes.