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.

Hydrogen Recycling Studies in Tokamaks and Other Facilities.- 1. Hydrogen Isotopes Retention in Fusion Reactor Plasma-facing Materials: An Abbreviated Review.- 2. Trapping Effect in Hydrogen Retention in Metals.- 3. Recent Progress in Tritium Codeposition Modeling.- 4. The Effect of Deuterium Ion Bombardment on the Optical Properties of Beryllium Mirrors.- 5. Hot Liner Divertor Concept Analysis of Dust Formation and Locations.- Hydrogen Sputtering, Retention, Codeposition in Graphite.- 6. Hydrogen Isotope Retention Analysis for Tokamak Plasma-facing Materials.- 7. Surface Microrelief Influence on Hydrogen Interaction with Materials.- Hydrogen Recycling in Liquid Metals.- 8. Deuterium Treatment Effects on Lithium and TiN-Lithium Sputtering in Solid and Liquid Phase.- 9. Helium Entrapment in Liquid Metal Plasma-facing Surfaces in Tokamak Fusion Reactors.- Fundamental Permeation Studies I.- 10. A Model for the Steady State Plasma- and Gas-driven Hydrogen Isotope Permeation through Multi-layer Metal.- 11. Effect of Hydrogen Sorption on Surface Morphology of Pyrolytic Graphite.- Fundamental Permeation Studies II.- 12. General Model of Hydrogen Transport through Solid Membranes.- 13. Influence of Hydrogen and Helium on Radiation Damage of Structural Materials.- Hydrogen Recycling in Tungsten, Niobium, and Nickel.- 14. Deuterium Retention in Tungsten and Tungsten Carbides Irradiated with D Ions.- 15. An Interpretation of the Retention of Low Energy Deuterium Ions in Tungsten.- General Hydrogen and Helium Issues and Other Metals.- 16. Hydrogen Interaction with TiN Films.- 17. Bimetallic Diffusion Membranes: Possible Use for Active Hydrogen Recycling Control.- 18. Surface Evolution of Nickel under He and H Ion Irradiation by means of Kelvin Probe.- Measurements and Control of Hydrogen Recycling I.- 19. Development of an Innovative Carbon-based Ceramic Material; Application in High Temperature, Neutron and Hydrogen Environment.- 20. Nonmonotone Temperature Dependence of Plasma Driven Permeation through Nb Membrane.- Measurements and Control of Hydrogen Recycling II.- 21. Usage of Hydrogen-saturated Getter for Sputtering Protection of Construction Elements in Vacuum-plasma Installations.- 22. Laser Induced Breakdown Spectroscopy Technique for In-situ Dust Detecting in a Next-step Tokamak.- Authors.