The field of soft tissue tumors is complex and challenging because of the large number of soft tissue tumor types; the often, and subtle, histologic differences between them; and the rarity of many soft tissue neoplasms. This AFIP fascicle provides a practical approach to the diagnosis of soft tissue tumors as well as a comprehensive morphological description and differential diagnosis for each of the well-characterized tumor types. Pertinent clinical and prognostic information accompanies the description of each tumor. Diagnostically useful immunohistochemical staining patterns and cytogenetic abnormalities with potential diagnostic utility are an integral part of the discussion. The following are a few of the topics discussed in detail: The importance of utilizing a managerial as well as a scientific classification when reporting on soft tissue tumors. Distinguishing morphologically bland, but clinically malignant, lesions such as low-grade fibromyxoid sarcoma from benign mimics. The reasons for retaining the category of the so-called fibrous histiocytomas. Myxoid lesions of the soft tissue. Atypical lipomatous tumors and dedifferentiated liposarcomas. Spindle cell/pleomorphic lipoma vs atypical lipomatous tumor. Problematic smooth muscle tumors of the soft tissues and retroperitoneum The differential diagnosis of small round blue cell tumors. Tumors of the soft tissues with constituent cells of an epithelioid phenotype. The morphologic features most useful in classifying vascular tumors. With 696 color illustrations and a comprehensive 507-page text, this fascicle represents a major source of information about soft tissue tumors. Peripheral nerve sheath tumors are covered in a separate fascicle.