This chapter reviews the current state of the art in membranes for direct methanol fuel cells (DMFCs), with a particular focus on research developments. The focus is exclusively on membranes; however, given the tight integration that is necessary between membranes and the adjacent fuel/oxidant distribution layers, catalysts, and support materials, there is some mention of these materials as they must necessarily be compatible with the selected membrane. To illustrate the basic principles of DMFC operations, the chapter presents a typical, liquid-feed cell with a cation exchange membrane. The most well-known and well-studied membrane materials for DMFCs are perfluorosulfonic acid membranes, such as Nafion. These macromolecules combine two different functionalities in a single macromolecule: first, the hydrophobic nature, which impacts the high chemical and thermal stability, and second, the hydrophilic sulfonic acid regions, which are responsible for the water update and ion exchange capability. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. All rights reserved.