A mathematical model that considers coupled mass transport, charge transport, and electrochemical reactions in an anion-exchange membrane (AEM) water electrolyzer is developed. Validations against the literature experimental data show that the present model can accurately predict the performance of the water electrolyzer. Numerical results show that the voltage loss in the electrolyzer is majorly due to the activation polarizations of hydrogen and oxygen evolution reactions. The effects of the exchange current density, the membrane thickness, and the liquid saturation on the performance are also studied; it is shown that the performance of the water electrolyzer improves with an increase in the exchange current density and liquid saturation, but with a decrease in the membrane thickness. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.