Capacitive Deionization (CDI) is an emerging, eco-friendly desalination technology gaining momentum. This review covers key topics in CDI, including electrode materials, cell architectures, selective ion removal, energy consumption, and salinity ranges. Key improvements include optimizing carbon materials with surface functional groups, heteroatom doping, and metal oxide modifications. The use of Faradaic materials has significantly increased CDI’s desalination capacity. Innovations in cell architecture from static to flow electrodes allow for continuous production, boosting energy efficiency and expanding CDI’s salinity range. Future research should focus on ion-selective mechanisms, electrode stability, hydraulic design, and economic and environmental assessments to enhance scalability and practical applications.