Autoimmune pancreatitis (AIP) is distinct from calcifying and obstructive forms of chronic pancreatitis. Clinically and histologically it has two distinct subsets: (i) lymphoplasmacytic sclerosing pancreatitis or type 1 AIP which appears to be a systemic disease characterised by abundant infiltration of affected organs with immunoglobulin G4 (IgG4)-positive plasma cells and (2) duct-centric or type 2 AIP characterised by granulocyte epithelial lesions in the pancreas without systemic involvement. In AIP a marked lymphoplasmacytic infiltrate that responds dramatically to steroid therapy suggests an autoimmune aetiology. However, the target autoantigen(s) and the effector cells in AIP remain speculative. Despite the consistent elevation in serum IgG4 levels and tissue infiltration with IgG4-positive plasma cells in type 1 AIP, the role of IgG4 in its pathogenesis remains unknown. Recent development of animal models of AIP will help improve our understanding of the pathogenesis of these newly described forms of chronic pancreatitis.