Perfluorosulfonic acid ionomers (PFSAs) are the benchmark materials used as proton-exchange membranes (PEMs) in fuel cells. Conventional PFSA membranes have a chemical structure consisting of a PTFE backbone with randomly distributed perfluoroether side chains that terminate with a sulfonic acid group. These polar -SO₃H groups, distributed within a matrix of non-polar PTFE segments, tend to aggregate forming a complex nanostructured network of hydrophilic domains. Further percolation of these domains (generally observed with increasing water content) provides pathways for efficient transport of protons (or other ions) and water in a variety of membrane-based electrochemical energy conversion and storage applications. To enhance or optimize the transport properties of a given PFSA, a variety of solvent casting and post-processing thermal treatments have been developed to facilitate molecular mobility during morphological development. In this presentation, we will focus on molecular-level considerations of the glass transition, T_g, of PFSAs with respect to thermal drying and annealing protocols used in conventional PFSA membrane processing. Using dynamic mechanical analysis (DMA), we have previously assigned the true T_g of H⁺-form Nafion^® to be associated with a weak β-relaxation observed near -20 °C. Recently, we have found that the β-relaxations in other PFSAs (e.g., 3M PFSA and Solvay’s Aquivion^®) can also be assigned to the glass transitions of these polymers. Nevertheless, the β-relaxations of all these PFSAs are weak in comparison to the dominant α-relaxation, associated with a transition from a physically crosslinked, H-bonded network to a dynamic network that allows for significant reorganization of the polar functionalities during thermal processing.