Since the appearance of the second series fascicle on this topic, there has been considerable growth in our knowledge of these neoplasms, including wider recognition of types of mesothelioma with unusual microscopic features or behavioral patterns. Recent progress in the application of immunohistochemistry has led to more accurate histological diagnosis of mesothelioma and has made it easier to recognize those nonmesothelial tumors mimicking mesothelioma. Nonetheless, hematoxylin and eosin-stained preparations remain the mainstay of diagnosis of serous membrane tumors. Thus, due emphasis is placed on conventional histological findings in this new fascicle, while at the same time expanding the coverage of important diagnostic tests such as immunohistochemistry. In addition to the malignant mesotheliomas, attention is given to other mesothelial-related tumors such as primary serous papillary carcinoma of the peritoneum, multicystic mesothelioma, intra-abdominal desmoplastic round cell tumor, adenomatoid tumor, localized fibrous tumor, and the so-called mesothelioma of the atrioventricular node. Concise tables depict such features as: the differential diagnosis of diffuse malignant mesothelioma; the comparison of histologic features of mesothelial hyperplasia, mesothelioma, and carcinoma; and the immunohistochemistry of peritoneal mesothelioma and serous carcinoma. The fascicle is 128 pages long and includes over 150 illustrations, 104 of which are in color. It should be an essential reference for pathologists in practice and in training.