Asphyxia is a broad term that refers to a variety of conditions that result in interference with the uptake or use of oxygen. A reduced concentration of oxygen in the blood that reaches the brain causes rapid loss of consciousness. Because the brain is the organ most sensitive to oxygen deprivation, it is the organ most affected in all types of asphyxia deaths. Clinical records suggest that cardiac function may continue for as long as 10 minutes after respiratory arrest. Continued heart activity after respiratory arrest provides an opportunity for resuscitation. This chapter describes four major categories of mechanisms of asphyxia and then discusses the specific mechanisms under those categories and how each causes death. One major category of asphyxia mechanism is compression of the neck, with or without blockage of the airway. Mechanisms of asphyxia in this category are hanging and strangulation. A second major mechanism of asphyxia is obstruction of the airway. This category encompasses smothering; foreign material lodged in the airway; swelling of the lining membranes of the throat, as in some allergic and inflammatory reactions, and postural asphyxia, also known as positional or traumatic asphyxia. A third major mechanism of asphyxia is compression of the chest, which interferes with respiratory movements. The fourth major mechanism of asphyxia is exclusion of oxygen due to depletion and replacement by another gas or as a result of chemical interference with its uptake and use. This can occur due to poisoning by carbon dioxide, carbon monoxide, or cyanide. Physical signs of each of the mechanisms of asphyxia are noted. Extensive photographic exhibits and 34 references