This edition represents a significant expansion of both the textual and illustrative material of the Third Series Fascicle. The numerous images reflect the authors’ belief that the “atlas” role that was the intent of the original Fascicles of the Armed Forces Institute of Pathology is of paramount importance in these works. At the same time, the current scope is no longer primarily that of a visual resource, but also a comprehensive guide to clinical, pathologic, immunohistochemical, molecular biologic, prognostic, and to a limited extent, therapeutic aspects of the various entities. For this reason, the authors have greatly expanded coverage of the immunohistochemical and molecular features of the various lesions, recognizing that such information is quickly supplemented by new observations. Nonetheless, they continue to believe that careful gross examination and routine light microscopic observations are the foundations for diagnosis of these neoplasms and neoplastic-like processes.