We review the key properties of Ca-doped LaNbO4 (LCNO) and related materials for use as proton conducting electrolyte, from the discovery of its proton conductivity, through developments of synthesis and production, anodes and cathodes, to demonstrations of it in laboratory fuel cells, exemplified through published and new results from a range of collaborative projects in Norway and Europe the last years. Important new knowledge has been obtained concerning the reliable synthesis of line compounds like LaNbO4, B-site doping and co-doping, grain boundary resistance, phase transformations, thin film fabrication, and electrodes for proton conducting ceramics. However, as LCNO still requires films too thin for reliable fabrication of large areas and operation over prolonged times, and since cathodes with acceptable electrocatalytic performance have not been identified, one must conclude that high-power fuel cells (and steam electrolysers) based on LCNO are not viable. (C) 2015 Elsevier B.V. All rights reserved.