Current designs for nuclear fusion reactors call for the use of the hydrogen isotopes deuterium and tritium as the fuel for energy producing fusion reactions. The use of tritium must be carefully controlled due to its cost and radioactivity, and there will be strict limits on the tritium inventory in fusion experiments or in a reactor. These concerns led the IAEA to organize a coordinated research project (CRP) on tritium inventory in fusion reactors, which brought together specialists in fusion materials and plasma–material interaction for exchange of information and coordination of research activities on interaction of tritium with plasma-facing materials. This volume of Atomic and Plasma–Material Interaction Data for Fusion is a result of that CRP. The key topics are tritium retention in fusion wall materials, measurements of tritium inventory and means to remove trapped tritium.