Mucinous neoplasms of the appendix are a heterogeneous group of neoplasms starting from simple mucoceles to complex pseudomyxoma peritonei. Considerable controversy exists on their pathologic classification and nomenclature. Accordingly, the goal of this text is to supply an up-to-date review of the pathology and imaging features of the mucinous neoplasms of the appendix including PMP. Cystic dilatation of the appendix results from luminal obstruction caused by either non-neoplastic or neoplastic conditions. Simple mucoceles are retention cysts which will result from an obstructing appendicolith, endometriosis, extrinsic compression or inflammatory conditions. Classification and taxonomy of mucinous neoplasms is complex and controversial. Neoplasms confined to the mucosa of the appendix are adenomas, whereas neoplasms extending beyond the appendix are often LAMNs or adenocarcinomas. Concerning findings at imaging, especially MDCT, include the presence of a soft tissue mass, irregular wall thickening and complications like rupture. Recognizing extra-appendiceal mucin is of utmost importance for correct staging and prognostication.