This book is devoted to exploring the complexities of the blood-brain barrier. The book begins by reviewing the historical experiments that led to the concept of a barrier protecting the brain from variations in the blood. Transport kinetics and carrier-mediated processes are described, and the mechanism by which molecules can cross the barrier is discussed. Ways in which the barrier can be disrupted and opened are covered as well. Subsequent chapters in the book describe the transport of glucose and amino acids into the central nervous systems, cover recent findings by which peptides and proteins are able to gain entry or are excluded from the brain, and analyze models that can be used for investigating how the blood-brain barrier can be disordered in neurological disease processes.