Both the CO poisoning problem on the anode and the slow oxygen reduction reaction kinetics on the cathode lead to significantly decreased output power and energy utilization efficiency and remain main obstacles hindering commercialization of proton-exchange membrane fuel cells (PEMFCs). A promising means to mitigate CO poisoning and to improve the oxidation reduction reaction (ORR) activity is through the use of platinum alloy catalysts. This article reviews recent developments in Pt alloy catalyst utilization and addresses activity comparisons and the relationship between activity and structure characteristics. The mechanisms for improved CO-tolerance and ORR activity are also discussed. Finally, theoretical studies on Pt alloy catalysts are discussed briefly.