Chapter starts with definition of dental caries. Then goes onto discuss about the various bacterial etiological agents for caries formation namely Streptococcus Mutans serotypes. Theories of caries formation are explained in detailed manner the three theories of caries aetiology are, (i) Acidogenic theory, (ii) Proteolysis Theory and (iii) Proteolysis–Chelation Theory. Pathophysiology of caries is explained with emphasis on critical pH. Clinical sites of caries formation and clinical features are explained for (i) Pit and Fissure caries, (ii) Smooth surface caries and (iii) Root surface caries. Histopathology of enamel and dentin caries is explained, with emphasis on various histological zones. Caries diagnosis and aids used in diagnosis like caries activity tests are explained. Preventive aspects of caries are explained in a detailed manner. Various classifications of caries are explained.