This paper presents an overview of some of the key challenges and issues that need to be overcome in the area of performance and durability to achieve commercial-viable PEM fuel cell technology(1). While there has been significant progress towards these objectives in the last few years, fundamental understanding of the factors resulting in performance loss and materials degradation is still lacking. Several key elements in overcoming these challenges, such as in situ diagnostic tools, modelling and simulation and accelerated stress tests are discussed. A general framework for the improvement of performance degradation and durability is presented in order to achieve the US DOE cost target of USD 30 kW(net)(-1) for the fuel cell stack, while advancing operational imperatives such as freeze start, higher temperature operation and reduced reliance on external humidification. (c) 2007 Elsevier B.V. All rights reserved.