We review our recent work on dealloyed nanoparticle electrocatalysts and address their synthesis, structural characterization and surface catalytic performance in low-temperature Polymer Electrolyte Membrane fuel cells (PEMFCs). The active form of the catalyst is obtained by voltammetric dealloying of non-noble metal rich Pt alloy precursors. In the dealloying process, the less noble precursor component, here Cu, is selectively removed from the surface of the precursor alloy particles and hence a Pt enriched particle shell is formed. Single fuel cell tests showed that, when used on the cathode of PEMFCs, dealloyed Pt catalysts show reactivities for the oxygen reduction reaction (ORR) which are up to 6 times higher than those of conventional pure Pt fuel cell catalysts. Similarly, the stability of dealloyed nanoparticle catalysts is superior to that of pure Pt particles. X-ray based structural and compositional studies suggested a core-shell particle structure as the active form of the catalyst consisting of a Pt enriched particle shell surrounding a Pt alloy core. At the present time, this catalyst system constitutes one of the most active fuel cell catalyst system reported in the literature.