The benefits of selenium (Se) in cancer prevention and treatment have been studied extensively for decades. The results of many in vitro and animal studies indicate that Se can effectively reduce the risk of cancers and decrease tumor growth. Compared to studies focusing on the initiation of cancer, there are considerably fewer reports concerning the potential use of Se in the prevention or control of metastasis. In this chapter, we summarize the current findings indicating that Se can affect several important steps in the metastastic process, including the maintenance of cell integrity, epithelial-mesenchymal transition (EMT), cell migration, cell invasion, extracellular matrix (ECM) degradation, and angiogenesis. These findings support the idea that Se can be a useful agent in managing metastasis. More studies are needed to fully understand the mechanisms by which Se regulates tumor development, and to determine the optimal concentration and formulae of the most effective Se molecules.