A compartment syndrome exists when increased pressure in a closed anatomic space threatens the viability of surrounding tissue. When this occurs in the abdominal cavity, the impact on end-organ function within and outside the cavity can be devastating. The abdominal compartment syndrome (ACS) is not a disease, but a clinic syndrome that has many causes and develops within many disease processes. Unlike many commonly encountered disease processes, which remain within the purview of a given discipline, intra-abdominal hypertension (IAH) and the ACS readily cross the usual barriers and may occur in any patient population regardless of age, illness, or injury. As a result, no one specific specialty can represent the wide variety of physicians, nurses, respiratory therapists, and other allied healthcare personnel who might encounter patients with IAH and/or ACS in their daily practice. The IAH is a graded phenomenon that can be acute or chronic, primary or secondary, and localized or generalized in character. The ACS on the contrary is not graded but rather considered as an “all or none” phenomenon. Recent animal and human data suggest that the adverse effects of elevated intra-abdominal pressure (IAP) can occur at lower levels than previously thought and even before the development of clinically overt ACS. This chapter will present a concise overview of the historic background, epidemiologic data, definitions, pathophysiologic implications, and treatment options for ACS.