The main results of the effect of neutron irradiation on beryllium, tungsten and carbon based materials are summarized in the paper in terms of changes of the material's structure and physical and mechanical properties. As a consequence of the material property changes, some of the plasma-material interaction phenomena could change significantly. The effect on phenomena such as bulk tritium retention, behaviour during thermal transient events, and changes of the thermal conductivity are discussed. Based on the available data, the subsequent influence of the neutron irradiation on the performance of the plasma facing materials in ITER has been analysed. The performance of the plasma facing materials at higher neutron fluence (e.g. DEMO) is also discussed. (C) 2003 Elsevier Science B.V. All rights reserved.