Metastasis contributes to poor prognosis in many types of cancer and is the leading cause of cancer-related deaths. Tumor cells metastasize to distant sites via the circulatory and lymphatic systems. In this review, we discuss the potential of circulating tumor cells for diagnosis and describe the experimental therapeutics that aim to target these disseminating cancer cells. We discuss the advantages and limitations of such strategies and how they may lead to the development of the next generation of antimetastasis treatments.