Water pollution and freshwater scarcity are two of the most important environmental problems faced by human around the globe in the 21st century. Capacitive deionization (CDI), as a promising electrochemical water treatment technology, has attracted large attention over the past decade for the facile removal of ions from water with the advantages of environmental friendliness, cost effectiveness, low energy consumption, and convenient electrode regeneration. Enormous progress has been made in the CDI research field and now CDI encompasses various cell architectures assembled with either capacitive electrodes or battery electrodes. These scientific advances are accompanied by a diverse application of CDI-based technologies. This work is intended to summarize the versatile applications of CDI and highlight the representative achievements in each of the applications primarily covering water desalination, water purification, water disinfection, resource recovery and synergistic combination with other technologies. Emerging application areas of CDI such as energy harvesting and CO2 capture are also presented. Lastly, the challenges and future outlook for CDI practical applications are discussed. This work should be of value in promoting CDI-based technologies to develop into a competitive option for coping with multiple water or energy-related issues. Display omitted •Versatile applications of CDI were comprehensively reviewed.•Representative achievements in each of the applications were highlighted.•Challenges and future outlook for CDI practical applications are discussed.