The first International Symposium on Theory and Applica- tion of Ion and Enzyme Electrodes in Biology and Medicine was organized at SchloB Reisensburg near Ulm in 1974. The concept of this meeting was to discuss the theory and applica- tion of carrier operated electrodes within an interdisciplinary group of investigators coming from physical chemistry, or- ganic chemistry, physiology, biochemistry and medicine. Be- cause of its interdisciplinary character, the Symposium proved to be very productive and further meetings based on the same principle were held at the Max-Planck-Institut fUr Systemphysiologie in Dortmund in 1977 and 1980. For the 1983 meeting it was decided to return to the ethe- real atmosphere of a castle (Burg Rabenstein) set in the beau- tiful surroundings of Swiss Franconia. Participation was re- stricted to those involved in the theoretical, experimental and clinical applications of ion selective electrodes. In this way a critical mass was achieved whereby an infor- mation transfer was induced between groups who had previ- ously had little or no communication with each other. We hope that this interdisciplinary spirit may encourage and stimulate those scientists and clinicians who are considering entering the field of ion investigations and that this book may serve as a compendium of current ion selective electrode methodology and ideas, together with their application in the- oretical fields, physiology and medicine.