In this chapter, we summarize some important parameters regarding the proton exchange membrane (PEM) in a direct methanol fuel cell (DMFC) system. The PEM mainly consists of a solid polymer that can be either natural or synthetic. Synthetic polymers are much easier to handle due to their natural, man-made production. The purpose is to present the type of membrane structure that is commonly governed in DMFC applications. Other than that, membrane fabrication methods, membrane characterization, and separation mechanisms that occur inside the polymer matrix are disclosed in this chapter. The potential applications of DMFC in various field is also explored. Therefore, by analyzing all of the above concerns, it was assumed that the understanding of DMFC systems could be further clarified, which is not only restricted to dense membranes, but also to porous membranes. © 2020 Elsevier Inc. All rights reserved.