Eph receptors are the largest receptor tyrosine kinase family of transmembrane proteins with an extracellular domain capable of recognizing signals from the cells' environment and influencing cell-cell interaction and cell migration. Ephrins are the ligands to Eph receptors and stimulate bi-directional signaling of the Eph/ephrin axis. Eph receptor and ephrin overexpression can result in tumorigenesis as related to tumor growth and survival and is associated with angiogenesis and metastasis in many types of human cancer. Recent data suggest that Eph/ephrin signaling could play an important role in the development of novel inhibition strategies and cancer treatments to potentially target this receptor tyrosine kinase and/or its ligand. A deeper understanding of the molecular basis for normal versus defective cell-cell interaction through the Eph/ephrin axis will enable the potential development of novel cancer treatments. This review emphasizes the biology of Eph/ephrin as well as the potential for novel targeted therapy through this pathway.