Superwettability is a centuries-old concept that has been rediscovered in past decades, largely owing to new understanding of the mechanisms of special wetting phenomena in nature. Combining multiscale structures and surface chemical compositions is crucial to fabricate interfacial materials with superwettability. In this Review, we detail the historical development and summarize the various combined superwetting states in superwettability systems. Nature-inspired design principles of superwettable materials are also briefly introduced. Superwettability systems can be extended from 2D surfaces to 0D nanoparticles, 1D fibres and channels, and 3D integrated materials. We discuss new phenomena and the advantages that superwettability-based systems have for chemical reactions and materials fabrication, including emerging applications that utilize single extreme wetting states or that combine two extreme wetting states. Finally, we provide our perspective for future research directions.