This chapter summarizes cementum biology knowledge, formation, types, composition, and clinical aspects. Two main types of cementum exist on human tooth roots. Acellular cementum (AC) covers cervical root surfaces and cellular cementum (CC) covers apical and furcation regions. Cementogenesis occurs during root formation following completion of the crown. Cementum formation includes deposition and mineralization of collagen fibers on root dentin surface by cementoblasts. The slow appositional growth of AC throughout life incorporates Sharpey’s fibers to anchor teeth to the alveolar bone. CC formation is initiated around the time the tooth enters occlusion. Cementum is composed of approximately 45-50% inorganic material by weight, primarily hydroxyapatite. The organic component includes multiple types of collagens and non-collagenous proteins such as bone sialoprotein and osteopontin, that may regulate mineralization and other properties. In considering the use of tooth root cementum to estimate ages of human samples, various circumstances may affect cementum structure, growth, or other properties and should be considered during analysis.