The global production of plastics made from non-renewable fossil feedstocks has grown more than 20-fold since 1964. While more than eight billion tons of plastics have been produced until today, only a small fraction is currently collected for recycling and large amounts of plastic waste are ending up in landfills and in the oceans. Pollution caused by accumulating plastic waste in the environment has become worldwide a serious problem. Synthetic polyesters such as polyethylene terephthalate (PET) have widespread use in food packaging materials, beverage bottles, coatings and fibres. Recently, it has been shown that post-consumer PET can be hydrolysed by microbial enzymes at mild reaction conditions in aqueous media. In a circular plastics economy, the resulting monomers can be recovered and re-used to manufacture PET products or other chemicals without depleting fossil feedstocks and damaging the environment. The enzymatic degradation of post-consumer plastics thereby represents an innovative, environmentally benign and sustainable alternative to conventional recycling processes. By the construction of powerful biocatalysts employing protein engineering techniques, a biocatalytic recycling of PET can be further developed towards industrial applications. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.