Non-ribosomal peptide synthesis is a vital source of many important natural products, including the glycopeptide antibiotics such as vancomycin. By removing the constraints imposed by ribosome-based peptide synthesis, non-ribosomal peptide synthesis can exploit a range of monomers far greater than standard proteinogenic amino acids: to date, more than 500 different monomers have been identified and these, combined with many further modifications, can have dramatic effects on the structural and biological diversity of these compounds. The enzymatic machinery that produces these compounds is a group of fascinating megaenzyme synthases known as non-ribosomal peptide synthetases (NRPSs). Utilising a modular architecture of repeating catalytic domains and combined with multiple interaction partners in trans, NRPSs have long been recognised as potential targets for enzymatic redesign to produce new, bioactive compounds. To date, this research has largely been hindered by a lack of understanding of how NRPSs function: my group aims to overcome these limitations by focusing on the characterisation of specific, important examples of NRPS biosynthesis. In this presentation I will showcase the results of our research glycopeptide antibiotic biosynthesis concerning two processes crucial for antibiotic activity: peptide halogenation and the oxidative cyclisation cascade.