The radiation damage in the materials is? a key parameter that eventually defines the life expectancy and safety operation of?the nuclear facilities. The time evolution and final appearance of material changes depend?on the type, intensity?and energy spectra of incident radiation?as well as?on the materials properties and ambient environment. Although this?process is not yet?completely understood, it has been established?that some material property changes are sensitive to the results of nuclear collisions (atom displacement and?gas production), while others are more sensitive to the effects of ionization. ?For the group of practically important materials with crystalline structure, such as metals, ceramics?and some alloys, the atom displacement cross section was found to be a reference?parameter?suitable for?characterization and comparison of the radiation damage induced by neutrons and charged particles. ?The so-called NRT-dpa standardproposed by Norget, Torrens and Robinson for evaluation of the number of displaced atoms? has been universally used since 1975. Although the usefulness of the NRT-dpa for correlating many radiation damage phenomena was recognized, its limitations were also demonstrated with?indications that other parameters?could be used to better correlate certain kinds of data. ?The development of specific damage models is best done within the materials community, based on information obtained from nuclear data researchers. For a given irradiation environment, these data need to include the primary knock-on atom (PKA) spectrum, nuclear transmutation rates (particularly gas production), and partitioning of the PKA energy into nuclear and electronic stopping effects.?This CRP engages participants from both the nuclear data and materials research communities and will?determine the best possible parameter (or a few parameters) for correlating damage from irradiation facilities with very different particle types and energy spectra, including fission and fusion reactors, charged particle accelerators, and spallation irradiation facilities. The essential progress?in the course of?CRP?is expected for crystalline materials (such as fuel UO2, structural metals, SiC), for which?the upgraded cross sections for the?primary damage (primary radiation defects and gas production)?will be produced.