Bacterial natural products display astounding structural diversity, which, in turn, endows them with a remarkable range of biological activities that are of significant value to modern society. Such structural features are generated by biosynthetic enzymes that construct core scaffolds or perform peripheral modifications, and can thus define natural product families, introduce pharmacophores and permit metabolic diversification. Modern genomics approaches have greatly enhanced our ability to access and characterize natural product pathways via sequence-similaritybased bioinformatics discovery strategies. However, many biosynthetic enzymes catalyse exceptional, unprecedented transformations that continue to defy functional prediction and remain hidden from us in bacterial (meta)genomic sequence data. In this Review, we highlight exciting examples of unusual enzymology that have been uncovered recently in the context of natural product biosynthesis. These suggest that much of the natural product diversity, including entire substance classes, awaits discovery. New approaches to lift the veil on the cryptic chemistries of the natural product universe are also discussed. Bacterial natural products (NPs) are specialized metabolites that encompass an extraordinary breadth of different biological activities, many of which are of considerable value to society. NPs or NP-inspired compounds represent ~65% of all small-molecule approved drugs 1 used in medicine to treat infectious diseases, cancers or as immunosuppressants 2 , and they are also applied extensively in agriculture 3. While NPs have been an extremely productive source of new leads for the chemicals that are integral to modern life, rapid increases in resistance to antibiotics, cancer chemotherapies and pesticides pose significant threats to medicine and agriculture 4,5 .