The biotechnological conversion of lignocellulosic biomass is a pivotal aspect in the development of overall sustainable and environmentally friendly biorefinery and valorisation processes of non-fossil biomass. Lipoxygenase (EC 1.13.11.x), a non-cellulolytic oxidizing enzyme normally working on linoleic acid metabolism, is demonstrated to catalyse the oxidative functionalization of lignin. Lipoxygenase was used for structurally altering the most important types of technical lignins. Most noteworthy oxidation is achieved by activation via a radical mechanism leading to both oxygen- and carbon-centred radicals.. Since this activation takes also place on the lignin backbone, the ketyl and benzyl radicals generated can be used to functionalise lignins via formation of carbon-carbon bonds.