This book presents the work of the RILEM TC 258-AAA WP3, and serves as a comprehensive review of the role of alkalis in concrete in relation with the alkali-silica reaction. Chapter 1 investigates different aspects of the reaction related with the prevention, the characterization and development with the time of the ASR and the factors of influence. Chapter 2 is an in-depth analysis of the internal alkalis in the concrete components, while the Chapter 3 is related with the alkalis of the external alkalis. Chapter 4 provides valuable information about the standardization and regulations to prevent and to taking actions to minimizing the degradation due to the ASR. Finally, the Annex examines different structures, mainly pavements with flat shape and low volume of concrete, and dams with a very big volume of massive concrete and different tensional areas.