Efficient degradation of recalcitrant waste requires using pretreatment prior to anaerobic digestion of the substrate. Pretreatment is a prerequisite method for reducing structural and compositional impediments of residues, particularly in terms of lignocellulosic and keratinrich biomass. As a result, the compounds become more accessible to enzymes, which significantly improves their conversion. This paper shortly reviews the current trends related to the techniques used for pretreatment of recalcitrant waste that enhance its digestibility. In the consecutive sections, different pretreatment methods (physical, physicochemical, chemical, biological as well as combined one) are described and their effects on improving the enzymatic hydrolysis of complex structures are discussed.