The interest in designing new nanocomposite proton exchange membranes (PEMs) with improved performance for high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) and direct methanol fuel cells (DMFCs) is fast growing. Carbonaceous nanomaterials such as carbon nanotubes (CNTs), graphene, and graphene oxide (GO) are attractive fillers for preparation of a variety of nanocomposite PEMs. Particularly, the incorporation of these nanofillers not only provides unique structures with high surface areas and more channels for proton transfer but also improves the proton conductivity and mechanical properties of the nanocomposite PEMs. This chapter provides a closer look at various structures of nanocomposite PEMs using CNTs, graphene, and GO as fillers. The latest progress in preparation of these types of nanocomposite membranes based on Nafion and other alternative membranes is comprehensively reviewed. The performance of these polymeric membranes in PEMFCs and DMFCs is addressed in comparison with their counterparts without fillers. © 2018 Elsevier Inc. All rights reserved.