The work presented here describes the design, fabrication, evaluation and use of miniaturised polymeric devices, for performing capillary isotachophoresis (CITP). CITP is an electrophoretic separation method that provides a simple technique for the analysis of ionic substances. The two principal advantages of CITP over capillary zone electrophoresis (CZE) are that it allows larger volumes of dilute sample solutions to be loaded into the separation channel and the electrolyte system can be chosen to eliminate sample matrix constituents which are not of interest. In addition CITP can be used as a preconcentration technique to provide a narrow sample band for subsequent on-line CZE separation. The devices are fabricated from silicone elastomer with on-chip conductivity detection. The resulting system has been used to separate simple mixtures of ions.