The scintigraphic technique to investigate the lymphatic system is based on a good knowledge of basic criteria in order to correctly interpret the findings. This article penetrates these criteria, updates the present knowledge, and covers basic science work and clinical applications. The anatomy, physiology, and pathology of the lymphatic system are covered. Basic criteria for the radiopharmaceuticals to be used are described as well as their quality control. The principles for lymphoscintigraphy are described. The dosimetry in lymphoscintigraphy as well as radiation risk is estimated for different procedures. Experimental animal studies are summarized. Clinical applications cover staging procedures for breast cancer, malignant melanoma, pelvic neoplasms, and lymphoma. Lymphadenoectomy follow-up studies are also included. The use of lymphoscintigraphy in radiotherapy dose planning is described as well as lymphatic function studies in, e.g., edema and lymph transplantations.