This chapter describes the decisive contribution of polymer-based materials to the propulsion of desalination technologies to increase the degree of water security worldwide in terms of sustainability. This approach provides a comprehensive description of how polymers, owing to their high permeability, selectivity, and chemical stability, have revolutionized membrane-based desalination techniques such as reverse osmosis (RO), forward osmosis (FO), and electrodialysis (ED). Emphasizing recent advances, this chapter discusses the development of higher-performance polymeric membranes, surface modification techniques to enhance antifouling properties, and nanomaterial incorporation to improve water flux and salt rejection. Additionally, the environmental implications of polymer use in desalination, including the material life cycle, energy efficiency, and waste disposal, are discussed. The chapter concludes by considering future directions and challenges and observing the potential of new polymer-based approaches, such as bio-based polymers and hybrid materials, to develop more efficient, cost-effective, and sustainable desalination technology.