 Petroleum-based plastics have replaced many natural materials, but their high recalcitrance results in long persistence in the environment and growing plastic waste. Microbial enzymes capable of modifying or degrading synthetic polymers are emerging as candidates for bio-catalytic plastic recycling processes to recover valuable raw materials in an environmentally sustainable way. This review focuses on microbial bio-catalysts involved in the degradation of polyethylene polystyrene polyurethane and PET discussing recent progress and challenges for their application in alternative plastic waste recycling processes. This article was authored by Ren Wei and Wolfgang Zimmermann.