The "Petrographic Atlas: Characterisation of Aggregates Regarding Potential Reactivity to Alkalis" is a specialized book that focuses on the identification of alkali-reactive rock types in concrete aggregates through thin-section petrography. This atlas complements the petrographic method described in RILEM AAR 1.1 and provides a comprehensive guide for assessing rock materials. It is particularly useful for professionals working in construction and materials science, as it supports the classification of rocks according to internationally recognized standards. The atlas addresses the identification of mineral components and their reactivity, emphasizing the importance of expertise and experience in the application of thin-section petrography. Additionally, it highlights the need to consider local criteria for the classification of aggregates to ensure accurate assessments.