There has been a dramatic increase in knowledge of tight junctions in the past decade. The molecular structure of tight junctions, cellular functions and the pathophysiological roles of tight junctions are becoming clear. Of the most important functions, the role of the cellular structure in cancer spread and drug delivery are increasingly realised. It is now clear that there are fundamental changes to tight junctions during the process of cancer development. Tight junctions are also critical to the metastatic process of cancer cells. The cellular structure is also crucial in drug therapies, namely, the permeability and bioavailability of the drugs, penetration of barriers such as the blood brain barrier. This current volume aims to summarise the current knowledge of tight junctions, their role in cancer and cancer metastasis and is of interest to scientists and clinicians.