The blood-brain barrier (BBB) creates and maintains the highly regulated extracellular environment of the CNS through three 'lines of defense'. (1) a physical barrier formed by tight junctions between endothelial cells of the brain capillaries and epithelial cells of both the choroid plexus and the arachnoid membrane. (2) transporters that mediate the efflux of compounds from brain to blood. And (3) an enzymatic barrier conferred by an enrichment of degradative enzymes in these endothelial and epithelial cells. The goal of this book is to provide readers with a comprehensive review of the state-of-the-art of efflux transport across the blood-brain barrier and to provide detailed 'food-for-thought' which will hopefully stimulate more research in this area in both the academic and industrial research communities.