Capacitive deionization, or CDI, uses porous electrodes is a new promising technique to remove salt from water by reversibly adsorbing ions in selective electrodes. The electrodes can be made of porous activated carbon, or of an intercalation material. Ion-exchange membranes make the technology more efficient in energy and removal capacity. CDI can be used not just to desalinate water, but also to selectively remove one metal ion from a mixture of other ions of the same charge sign. Novel developments in CDI include the use of chemically modified carbon electrodes, application of flowing carbon slurries and fluidized beds, and the use of optimized charge/discharge schemes. Wetsus plays a prominent role in CDI research worldwide and is founder of the international working group on CDI, see www.cdi-electrosorption.org. In the theme the CDI-technology is further developed.