Lymphatics are a unidirectional transport system that carries fluid from the interstitial space and back into the blood stream. Initial lymphatics take up not only fluid but also high-molecular-weight substances, such as plasma proteins and hyaluronan; immune cells, such as lymphocytes, macrophages, and dendritic cells; and colloidal particles, such as carbon particles, bacteria, and tattoo dye. Interstitially injected colloidal particles are known to accumulate in the regional lymph nodes. This phenomenon is applied to find sentinel lymph nodes in cancer patients. Lymph flow rate and composition are influenced by interstitial fluid, lymphatic pump activity, and intra-lymphatic pressure. Lymph composition is changed during its flow downstream. In this review, the main focus is on the mechanisms of lymph formation at the initial lymphatics and lymph transport through the collecting lymphatics and lymph nodes. (*English Translation of J Jpn Coll Angiol, 2008, 48: 113-123.)