Acute pancreatitis is defined as an acute inflammatory process of the pancreas with variable involvement of peripancreatic tissues or remote organ systems. This article reports the current classification, definition and terminology, epidemiology and etiology, pathogenesis and pathological findings, clinical and laboratory findings, and finally imaging findings of acute pancreatitis with emphasis on cross-sectional imaging modalities such as ultrasound, computed tomography, and magnetic resonance imaging.