Malignant soft tissue tumors are somewhat rare, and thus sufficient experience in diagnostics and therapy of these sarcomas is available as a rule only at specialist centers. The gold standard of morphological diagnosis is still represented by evaluation of HE-stained histological sections. However modern methods of examination are also helpful in diagnosis. Because immunohistochemistry is now used routinely, emphasis in this article is laid on molecular methods with special reference to fluorescence in-situ hybridization (FISH) and reverse transcriptase polymerase chain reaction. Principles of the WHO soft tissue tumor classification are explained, and the changed or expanded interpretation of some tumor entities is illustrated using the example of atypical lipomatous tumors, so-called malignant fibrous histiocytomas and hemangiopericytomas, fibrosarcomas, and inflammatory myofibroblastic tumors.