The Sentinel Lymph Node Concept is evaluated from the points of view of pathology, radiodiagnosis and nuclear medicine diagnostics, surgical treatment and clinical oncology. The concept and its practical applications are analyzed for breast cancer, malignant melanoma, tumors of the face, oropharynx, lung, gastrointestinal and urogenital tracts. The first part of the book describes the function and use of the nuclear medicine equipment, the tracers used, colloid solutions and modern developments in histological and immunohistochemical lymph node investigations, as well as possible pitfalls. The consequences of false-negative results are clearly delineated. In the second part, specific tumor-related problems are described.