Presence of multinucleate giant cells of numerous/various types are frequently encountered in histo-pathological investigation of oral and maxillofacial lesions. These include the common occurrence of foreign-body-type giant cells in some reactive lesions and giant cells associated with granulomatous inflammation as a consequence of infection. Giant cell-associated lesions of the orofacial region range clinically from slowly growing asymptomatic radiolucency discovered on routine radiographs, to a rapidly expanding aggressive tumours, characterized by pain, root resorption and a high rate of recurrence. This book reviews the basic information regarding the mechanism of formation and morphology of giant cells, its clinical, histopathological and significance in the associated giant cell lesions of the oral cavity. The classification of this group of lesions remains in dilemma because for lesions such as in cases of central giant cell granulomas of the jaw, the true nature or cause of the lesions has not been established.