Intraductal papillary mucinous neoplasms (IPMN) are mucinous cystic tumors of the pancreas, which were first classified into a unified diagnosis by the World Health Organization in 1996. These lesions originate from the cells of the pancreatic ductal system and may grossly or microscopically involve the pancreatic ducts in a diffuse or multifocal fashion. As experience with IPMN increases, it is becoming more evident that this process presents as a spectrum of neoplasia with significant variation regarding the clinical and radiologic presentation, malignant potential, and disease-specific outcome. IPMN encompasses a spectrum of precursor lesions, from adenoma to intraductal carcinoma to invasive cancer, with molecular data supporting the premise that this dysplastic process has the potential to progress from low-grade dysplasia to invasive carcinoma. Controversy over the management of IPMN exists because of the difficulty in obtaining a preoperative histologic diagnosis, the broad spectrum of neoplasia, the lack of understanding as to the frequency and time to malignant progression. This article describes the radiologic and histopathologic classification system of IPMN; the biologic behavior of these lesions, and the diagnostic testing most commonly used, and discusses the current treatment controversies.