This chapter describes one of the most important parts of a human body — the mouth. The mouth comprises the oral cavity including the vestibule, lips, cheek, palate, gingiva, and glands, teeth and tongue. The oropharynx comprises of the soft-palate, tonsillar fossa and palatine tonsil. The majority of soft tissue lesions in the oral cavity represent infectious, traumatic, or reactive processes rather than neoplasms and the precise etiology can often be determined through a careful history and clinical examination. The mucosal patches, which are common among adults, can be due to leukoplakia (white), erythroplakia (reddish) or due to infections (oral-thrush or candidiasis). The whitish-patch in thrush can be removed reveal to a bleeding mucosal surface. The chapter briefly discusses various types of mouth diseases, including different types of ulcers and malignant developments and presents the clinical features associated with these diseases.