Acute mesenteric ischemia (AMI) is an abdominal emergency characterized by a sudden decrease in blood flow to meet the metabolic demands of bowel. AMI is uncommon but associated with high morbidity and mortality. Imaging plays a decisive role in early diagnosis and management because the symptoms of AMI are often nonspecific without specific laboratory tests or serologic biomarkers for early diagnosis. AMI comprises distinct entities with unique pathophysiology, imaging features, and management strategies. The basic causal mechanisms underlying AMI are inadequate inflow (arterial occlusion), inadequate outflow (mesenteric venous occlusion), global hypoperfusion (nonobstructive mesenteric ischemia [NOMI]), and strangulating bowel obstruction. Identifying transmural necrosis is critical for all causes of AMI. The authors review the foundational anatomy and pathophysiology of AMI, its distinct imaging features, and a systematic approach to AMI with emphasis on up-to-date imaging findings predictive of transmural necrosis. They emphasize a pathophysiology-based approach to AMI rather than a semiology-based approach (ie, patterns and signs) because the imaging features, significance, and predictive value of the imaging findings vary based on the underlying cause of AMI, with arterial occlusive AMI and NOMI having worse prognosis than mesenteric venous AMI. The authors highlight the specific vascular, bowel, and extraintestinal findings for each type of AMI with emphasis on imaging predictors of transmural bowel necrosis and address points of confusion to equip interpreting radiologists with a foundational understanding of AMI.