Petrographic quantitative analyses using the RILEM AAR-1 method were performed on a representative number of concrete aggregates from diverse Italian geological settings, in order to determine typologies and contents of potentially alkali-silica reactive phases. The aggregate characterization was completed with XRF and XRPD analyses, coupled with the geological data of each deposit. The results of these analyses allowed to evaluate the potential reactivity of the Italian aggregates investigated, on the basis of the classification proposed by the RILEM method (Class I-very unlikely to be alkali-reactive; Class II-potentially alkali-reactive or alkali-reactivity uncertain; Class III-very likely to be alkali-reactive). Italian reactive aggregates are related to the presence of microcrystalline and cryptocrystalline silica, generally defined as chert or flint, which is present in various sedimentary rocks, mostly carbonates, but also in siliciclastic rocks, and alluvial deposits derived from the erosion of the Alpine and Apennines mountain belts. The strained quartz with undulatory extinction, mainly associated with metamorphic rocks and the amorphous glassy phase of volcanic rocks, are also ASR susceptible, although to a much lesser extent. Local reports attest to widespread case histories of serious ASR damages in concrete mostly along the Adriatic coast.