The lymphatic system serves as the primary route for the metastasis of many cancers and the extent of lymph node involvement is the most important indicator of tumor aggressiveness. Despite the apparent importance of the lymphatic vessels for tumor dissemination, it has remained unclear whether activation of lymphatic endothelial cells may affect tumor progression and metastasis and the molecular mechanisms of lymphangiogenesis are just beginning to be elucidated. This overview describes the unique structural and functional characteristics of the lymphatic vessels that render them particularly suitable for invasion by tumor cells and for their efficient transport to lymph nodes. Recent evidence indicates occurrence of tumor lymphangiogenesis and its correlation with metastasis. Molecular regulation of tumor lymphangiogenesis, its significance for tumor metastasis, and implications for cancer therapy are discussed.