Microbial fuel cells (MFCs) are a promising technology for sustainable production of alternative energy and waste treatment. The performance of microbial fuel cells is severely affected by limitations on irreversible reactions and processes in the anode and the cathode compartments. The purpose of this paper is to review the cathodic limitations MFCs and provide an overview on cathodic activation, ohmic and mass transport losses and substrate crossover. Recent studies that have addressed these limitations and explored approaches for improvement are also discussed. MFCs still face many challenges but with consistent advances, especially with respect to the cathode, performance can continue to improve. (C) 2008 Elsevier B.V. All rights reserved.