Global demandDemand for critical minerals will continue to increase as the world moves towards electrification and batteryBattery storage, with battery materialsBattery materials being a major driver for nickelNickel and cobaltCobalt demandDemand. Concurrently, global reserves of high-grade Ni and Co ores are declining, and the supplySupply of these metalsMetals is increasingly regionally concentrated: > 70% of cobaltCobalt is mined in the Democratic Republic of Congo and > 50% of nickelNickel is mined in IndonesiaIndonesia. DemandDemand for new sources and a diversified supplySupply chain has renewed interest in deep-sea mining of polymetallic nodulesPolymetallic nodules as an alternative source of critical minerals, particularly Cu, Ni, Co, Mn, and rare earth elements (REE). There has been considerable research and developmentDevelopment related to the sustainable harvesting of nodules from the seabed, and attention to the extractionExtraction of critical minerals from the harvested nodules has recently regained momentum. Advancements in process technologyTechnology are required to extract value from these nodules, specifically extractionExtraction flowsheetsFlowsheet for Ni and Co that are environmentally and economically competitive with land deposits. Potential processingProcessing routes to produce Ni and Co from sea nodulesSea nodules, as well as other by-products, are reviewed here. Commentary is also provided on the relative advantages of hydrometallurgical, pyrometallurgical, and combined hydrometallurgical and pyrometallurgical processingProcessing technologiesTechnology, along with the inherent processingProcessing challenges presented by this unique resource.