In recent years, amidst a global thrust toward clean energy research, electrochemical energy conversion systems, i.e., fuel cells, have received significant attention. Among the different types of fuel cells, the polymer electrolyte fuel cell (PEFC) is being considered as the primary candidate for variety of applications. In the PEFC, the electrode is a key component where the electrochemical reaction occurs. The electrode is the host to multi-scale, coupled physicochemical interactions including charge, liquid/vapor/gas transport inside a porous microstructure, which affect the overall cell performance. In this chapter, a mesoscopic modeling framework is presented in order to elucidate the intricate microstructure–transport–performance interplay inherent in the PEFC electrode.