Increasing demand for energy, energy security and the need to minimize the impact on the environment related to energy are the major drivers for the research and development of alternative energy technologies. Polymer electrolyte membrane (PEM) fuel cells are a promising alternative technology. However, their performance, in other words efficiency, can be hindered severely by the presence of contaminants. Impurities in the oxidant and fuel feeds act as barriers to the oxygen reduction and hydrogen oxidation. These impurities arise from the use of atmospheric air as the oxidant and hydrogen from reformate as the fuel. The electrolyte membrane can be attacked by ions originating from the cell components. These ions decrease the mechanical and chemical stability of the membrane resulting in the decrease of proton conductivity and reactant crossover. Due to the severity of these poisoning phenomena, much work has been dedicated to understanding their chemical kinetics, their effects and mitigation methods. This paper provides a comprehensive review of the experimental, analytical and numerical work devoted to understanding the contamination of the cathode, electrolyte membrane and anode. A summary of future directions and research topics is also given. (C) 2010 Elsevier Ltd. All rights reserved.