Pressure-driven membrane desalination (PMD), such as reverse osmosis or nanofiltration, is an energy-efficient technology that addresses water shortages by using saline waters to augment freshwater supplies. This Primer describes several key methodological aspects of PMD, including membrane fabrication, characterization and performance evaluation; system modelling; process configurations; and applications. Thin-film composite polyamide membranes represent the state of the art in reverse osmosis and nanofiltration membranes and are the focus of the membrane development discussion. First, thin-film composite polyamide membrane fabrication using interfacial polymerization and alternative methods is discussed, followed by an exploration of techniques for characterizing the morphological, structural and interfacial properties. Experimental procedures and model frameworks for evaluating membrane performance are introduced, noting caveats in data collection, interpretation and reproducibility, with best practices recommended. Additionally, the general method for modelling the module-scale behaviour of PMD processes is introduced, alongside process configurations for existing and emerging applications. Finally, an outlook for the development of PMD is provided, highlighting the most meaningful directions for future research to further advance PMD beyond the current state of the art.