INTRODUCTION The maxilla and mandible – the upper and lower jaws, respectively – form an important part of the bony facial skeleton and are unique in that they consist, in part, of the alveolar process which has the sole purpose of supporting the teeth. The teeth develop within the deeper part of the jaws and erupt up through the alveolar process, coming to lie within the tooth socket, suspended by the periodontal ligament which lies between the bony tooth socket and the cementum of the tooth root. The crown of the erupted tooth is cuffed at the neck by gingival mucoperiosteum and this junction of hard and soft tissues is a potential source of infection and inammation. The inammation can stimulate odontogenic epithelial remnants left after tooth development leading to the inammatory radicular cyst, the most common type of cyst affecting the jaws. In addition, other types of odontogenic epithelial residues may give rise to developmental odontogenic cysts. The odontogenic cysts, being unique to the jaws, form a major part of this chapter. Also covered are the non-odontogenic cysts which arise from embryonic epithelial residues found within canals running through the facial bones or entrapped at lines of bone fusion. The non-odontogenic cysts are less common but important in the differential diagnosis of cystic lesions. Non-epithelialized bone cysts are also covered since, although they are rare within the jaws compared to the long bones, they are important in the differential diagnosis of cysts of the facial skeleton.