The reliable and reproducible detection of dental caries by clinical examination has been recognized as a problem for decades with very variable approaches being taken to recognize and stage lesions along the continuum of caries--from very small initial lesions, just visible to the human eye, through more established white- and brown-spot lesions, to shadowing beneath the enamel and different extents of cavitation. Clinical caries lesion detection implies some objective method of determining whether or not disease is present, and many systems have been developed to improve the objectivity of examiners. The existence of a large number of different systems, using different definitions of caries detection thresholds, lesion staging and examination conditions has led to problems in comparing between studies and communicating across different dental domains. The International Caries Detection and Assessment System (ICDAS) has been developed from the best elements of previously published systems and is based upon the most robust evidence currently available to address the incompatibility of the systems currently used across the full breadth of cariology. The inherently visual ICDAS lesion detection codes are outlined for use with primary coronal caries, caries adjacent to restorations and sealants and for root surface caries. The ICDAS detection codes for primary coronal caries have been demonstrated to have the capability to record both enamel and dentinal caries in a reliable, valid and reproducible manner in both permanent and deciduous teeth and are being adopted increasingly in the domains of research, epidemiology, clinical practice and education.