Recently, the original Atlanta classification of 1992 was revised and updated by the Working Group using a web-based consultative process involving multiple international pancreatic societies. The new understanding of the disease, its natural history, and objective description and classification of pancreatic and peripancreatic fluid collections make this new 2012 classification a potentially valuable means of international communication and interest. This revised classification identifies 2 phases of acute pancreatitis - early (first 1 or 2 weeks) and late (thereafter). Acute pancreatitis can be either edematous interstitial pancreatitis or necrotizing pancreatitis, the latter involving necrosis of the pancreatic parenchyma and peripancreatic tissues (most common), pancreatic parenchyma alone (least common), or just the peripancreatic tissues (~20%). Severity of the disease is categorized into 3 levels: mild, moderately severe, and severe. Mild acute pancreatitis lacks both organ failure (as classified by the modified Marshal scoring system) and local or systemic complications. Moderately severe acute pancreatitis has transient organ failure (organ failure of <2 days), local complications, and/or exacerbation of coexistent disease. Severe acute pancreatitis is defined by the presence of persistent organ failure (organ failure that persists for ≥2 days). Local complications are defined by objective criteria based primarily on contrast-enhanced computed tomography; these local complications are classified as acute peripancreatic fluid collections, pseudocyst (which are very rare in acute pancreatitis), acute (pancreatic/peripancreatic) necrotic collection, and walled-off necrosis. This classification will help the clinician to predict the outcome of patients with acute pancreatitis and will allow comparison of patients and disease treatment/management across countries and practices.