This chapter provides information on the aqueous chemistry of various biogenic products in the presence of the most relevant elements present in concrete. It examines, in generic terms, the various mechanisms that can lead to deterioration of concrete through chemical reaction. The chapter also provides the introduction to the reader regarding some of the concepts used to characterize the substance behaviours. These are acidic strength, the formation of metal complexes in solution and the solubility product. The chapter employs a form of solubility diagram to illustrate the influence of the substances on cementitious systems. Concrete exposed to acids may undergo deterioration as a result of the accelerated leaching of chemical constituents in the cement matrix, and possibly also in the aggregate. This can occur by two mechanisms: acidolysis and complexolysis. Acidolysis involves the reaction of hydration products with the acid to yield soluble ions. Complexolysis is an enhanced leaching of the cement resulting from the formation of strong complexes.