A compendium representing the current state of the art in the modelling, simulation and physics of the interaction of hydrogen and helium with plasma facing materials in fusion reactors. This is the topic that will determine the success of the production of energy by future Tokamak reactors and it is here discussed by the world's experts. Topics covered are recycling of hydrogen isotopes; wall fuelling and wall pumping; active control of hydrogen recycling; hydrogen and helium behaviour in solids and liquid metals; and databases for recycling.Proceedings of the NATO Advanced Research Workshop on Hydrogen Isotope Recycling at Plasma Facing Materials in Fusion Reactors, Argonne, Illinois, USA from 22-24 August 2001A compendium representing the current state of the art in the modelling, simulation and physics of the interaction of hydrogen and helium with plasma facing materials in fusion reactors. This is the topic that will determine the success of the production of energy by future Tokamak reactors and it is here discussed by the world's experts. Topics covered are recycling of hydrogen isotopes; wall fuelling and wall pumping; active control of hydrogen recycling; hydrogen and helium behaviour in solids and liquid metals; and databases for recycling.Preface. 1. Hydrogen Isotopes Retention in Fusion Reactor Plasma-facing Materials: An Abbreviated Review; R.A. Causey, T.J. Venhaus. 2. Trapping Effect in Hydrogen Retention in Metals; O.V. Ogorodnikova. 3. Recent Progress in Tritium Codeposition Modeling; J.N. Brooks. 4. The Effect of Deuterium Ion Bombardment on the Optical Properties of Beryllium Mirrors; L.A. Jacobson, et al. 5. Hot Liner Divertor Concept Analysis of Dust Formation and Locations; V.M. Kozhevin. 6. Hydrogen Isotope Retention Analysis for Tokamak Plasma-facing Materials; T.A. Burtseva. 7. Surface Microrelief Influence on Hydrogen Interaction with Materials; A.V. Golubeva, et al. 8.Deuterium Treatment Effects on Lithium and TiN-Lithium Spl³k