Giant cells are mononucleated or multinucleated cells, which are very big as compared to other cells found in the tissue with nuclei varying from one to 100. In long standing infection or chronic inflammation the lymphocytes get converted into macrophages which fuse together and form multinucleated giant cells. A number of cystic, metabolic, osteodystrophic, microbial, tumour and tumour like lesions of the oral cavity show characteristic giant cells, which makes their diagnosis simpler. This book provides the features of the different giant cell lesions of the oral cavity.