Solid state ionic materials and devices are being used in medicine in many ways. A brief initial introduction to the materials, the devices and the pertinent electrophysiological and clinical aspects is presented. To exemplify the breadth of SSI material and device applications, an overview is given of three main areas: Biomedical applications of solid state power sources; biofuel cells; and iontophoretic and related devices used for controlled transdermal drug delivery and monitoring of physiological parameters. (c) 2006 Elsevier B.V. All rights reserved.