Given the energy problem that our society is facing, interest has been growing in the so-called hydrogen economy. In this system, fuel cells play an essential part. This paper gives an overview of the different materials currently thought to be potential proton exchange membrane materials for fuel cells operated at medium temperatures (100-200 degrees C). This includes perfluorosulfonic acid (PFSA) membranes like Nafion (R) but also its main competitors, as well as the solid acids. Indication of the main fundamental research directions for these materials will be given. The most frequently used experimental techniques to study the morphology of these membrane materials and their proton conduction mechanisms and water transport will be reviewed and presented. The aim of this review is double: to help scientists and science managers not yet in this field to easily gain an overview of the state-of-the-art membrane materials and the experimental techniques used to study them; and to give insight to scientists already carrying out research on membrane materials on how to extend their research either on other materials or with other experimental techniques. (C) 2010 Elsevier Ltd. All rights reserved.