Nafion is a perfluorinated sulfonic acid resin (PFSA), which was developed by the E. I. DuPont Company. Owing to its stability, superior mechanical properties, high chemical inertness, and proton conductivity, Nafion is currently used in commercial membranes and catalyst layers of fuel cells. This article overviews the structure, morphology, and mechanical and electrochemical properties of Nafion. In addition, important research as well as practical industrial applications, such as brine electrolysis, chlor‐alkali cells, salt splitting, clean power generation by Nafion polymer electrolyte fuel cells, batteries, gas separation, gas sensors, and electrodialysis, is also presented.