Technically, the oral cavity consists of the vestibule between the lips and cheeks externally and the teeth and alveolar processes internally and the larger oral cavity proper located internal to the dental arches. In clinical practice, the whole mouth is simply referred to as the oral cavity, but ‘vestibule’ is used for the specific area defined above. For charting of teeth and similar dental procedures, the mouth is divided into quadrants—upper right and left and lower right and left with the midline and occlusal surfaces of the teeth forming the dividing lines. It is a crucial skill for dental students and practitioners to recognize the naked eye appearance of the structures in a normal healthy mouth and variations that occur; abnormal appearances can then be recognized, diagnosed, and treated successfully. Much of the macroscopical appearance is determined by the underlying gross anatomy so this must be understood too. The best way to examine the interior of the mouth is on a subject seated in a dental chair with clinical lighting and the use of a tongue spatula and a dental mirror where necessary. However, you will be able to see most of the important features by examining the inside of your own mouth in a well-lit household mirror. The following description and illustrations apply to an adult mouth with a full secondary (permanent) dentition of two incisors, one canine, two premolars, and three molars in each quadrant, making 32 teeth in total. Apart from size, the major differences in childrens’ mouths are in the dentition. The primary (deciduous) dentition erupts into the oral cavity between the age of 6 months and 2 years. It comprises two incisors, one canine, and two molars in each quadrant, giving a total of 20 teeth. Most of the teeth of the secondary dentition erupt between the ages of 6 to 12, replacing the primary teeth; a combination of primary and secondary teeth, a mixed dentition, is found between these ages. Primary incisors and canines are replaced by their permanent successors, but the deciduous molars are succeeded by the permanent premolars; the three permanent molars in each quadrant are additional teeth.