Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are frequently encountered in critically ill patients and carry a high morbidity and mortality risk. Despite these facts, IAH/ACS are still overlooked by many physicians and therefore timely diagnosis is not made and treatment is often inadequate. All clinicians should be aware of the risk factors predicting IAH/ACS, the profound implications and derangements on all organ systems, the clinical presentation, the appropriate measurement of intra-abdominal pressure to detect IAH/ACS and the current treatment options for these detrimental syndromes. This comprehensive review provides knowledge about known facts, unresolved issues and future directions for research to improve patient survival and long-term outcome.