The selectins are a family of intercellular adhesion molecules that mediate the initial adhesion of leukocytes to the endothelia of blood vessels during inflammation. Recently, accumulating evidences indicate that the selectins play a crucial role during metastasis. The major mechanism is to mediate the initial adhesion of tumor cells to platelets and vascular endothelia. In addition, selectins and their ligands can also facilitate metastasis as signal molecules. In the future, selectins and their ligands will provide good possibilities as serum diagnostic markers for monitoring tumor and tumor metastasis. Furthermore, by inhibiting the interactions between selectins and their ligands, or by blocking the signaling pathways that lead to the expression of selectins, tumor metastasis would be prevented.