The prospect of increasing use of various types of continuous ion exchange equipment means that design techniques should be developed and tested with the objectives of formulating appropriate laboratory and pilot plant experiments, interpreting results fully, and making design proposals for large scale plants for purposes of cost comparison. The present state of the art is reviewed assuming that the reader has a basic knowledge of ion exchange technology and the various limitations and deficiencies are outlined. These mainly concern the validity of assumptions, the lack of diffusion coefficient data for design purposes and the mathematical difficulties associated with multi-component ion exchange. A particular area requiring further attention is the design of regeneration and rinse columns. A design method for these columns and the interaction between them is considered in order to find optimum sizes.