This paper reviews possible hydrogen devices using a proton-conducting ceramic and describes the prospect of hydrogen technology utilizing these devices. Solid-state protonic devices can be classified into two categories: the devices utilizing electromotive force (EMF) and the ones utilizing preferential transport of protons. Galvanic cell type hydrogen sensors and fuel cells belong to the former, and hydrogen pump, steam electrolyzer and membrane reactors to the latter. Various kinds of modifications can be derived, in principle, from these devices. In this paper, the working principles of these devices and status of the development are reviewed touching the future prospect of applications. In addition, the recent studies and the possibilities of protonic devices for nuclear fusion process in the future are introduced. (C) 2003 Elsevier B.V. All rights reserved.