Odontogenic infection is an infection caused by a tooth. The term is derived from the ancient Greek words odonto (tooth) and genos (birth). Knowledge of microbiology and pathophysiology is crucial to understanding diagnostics and treatment of ofontogenic infection. The nature of anatomical boudaries and fragile maxillofacial structures create conditions for unobstructed spread of the infection. Initially, each infection is localized and closely related to the tooth pathogen. If left untreated, the pus propagates from primary afflicted spaces and complications develop. Secondary spaces are sites which are not initially affected by the infection, and if they become infected with the infection, local complications develop. In terms of the localization, they are divided into maxillary and mandibular spaces, and the borders are closely related to the anatomy, making the identification of the trigger tooth easy. They are clinically manifested by the typical symptoms of inflammation (tumor, dolor calor, rubor, funtio laesa) and, due to the proximity of the masticatory muscles, to a lesser or more pronounced trismus. The swelling compromises oral functions (chewing, swallowing, and speech). In most cases general symptoms of the inflammation are present. Local complications are treated on an outpatient basis and correct elimination of the causative agent results in complete recovery of the patient. Systemic complications are the consequence of the effect of the infection on distant organ systems. They develop after anatomical communications are established between secondary spaces and organ systems. Maxillary secondary infections most often ascend as they travel via copious venous anastomoses to the cranial structures. Infection of the mandibular teeth tends to descend directly via fascial planes, thereby affecting the thoracic organs. All complications are considered emergency conditions which require hospitalization. Such infections are life-threatening and they manifest with positive general symptoms. The treatment requires comprehensive differential diagnosis and a multidisciplinary approach.