In addition to their basic applications, i.e. sensors, separators, fuel cells and hydrogen pumps, high temperature proton conductors have been also used in the construction of proton conducting membrane cell-reactors in which catalytic hydro- and dehydrogenations are optimized in terms of their yield or selectivity to the desired product. The fundamental operating principles, results in technologically important reactions, and the hurdles to be overcome in order to promote these systems into an industrial scale, are discussed. (C) 2006 Elsevier B.V. All rights reserved.