Concrete structures are susceptible to a variety of chemical reactions, with AAR and ISA being two of the most common processes that cause structures to deteriorate their durability. Improving the durability of concrete structures is an important and scientific challenge. AAR and ISA are slow processes, becoming noticeable 20 to 30 years after construction. This paper presents fundamental theory and concepts of AAR and ISA in concrete. AAR and ISA are caused due to the reactivity of aggregates along with alkalis and sulphates. Based on the previous research, AAR and ISA are further divided into Alkali Silica Reaction (ASR), Alkali Carbonate Reaction (ACR), Delayed Ettringite Formation (DEF) and Thaumasite Sulphate Attack (TSA). We can detect AAR and ISA with the help of evaluation methods. The aspects of AAR and ISA discussed include source, mechanism, investigations and preventive measures.