Dental calculus is an adherent, calcified or calcifying mass that forms on the surfaces of teeth and dental appliances. It is covered on its external surface by vital, tightly adherent, and nonmineralized plaque. Depending upon the position of calculus in relation to the marginal gingiva, it is classified as supragingival calculus and subgingival calculus. This chapter covers the structure, composition, differences between supra- and subgingival calculus, attachment to the tooth surface, formation of calculus, clinical assessment of calculus, pathogenic potential of calculus in periodontal diseases, classification of anticalculus agents, and other contributing etiological factors including food impaction.