Oral cavity includes mouth, tongue, lips, palate and tonsils. This chapter describes developmental, inflammatory and infective diseases affecting various parts of oral cavity. Neoplastic lesions (benign and malignant) involving oral cavity are described in details. It includes premalignant oral lesions, clinical features, investigations, staging and treatment of oral cancers with outlines of reconstruction following surgical excision. In the end, detailed method of clinical examination of oral cavity is described with the help of clinical photographs.