For many years, the immune and central nervous systems were thought to function independently with little or no interaction between the two. This view has und- gone dramatic changes over the past three decades. Indeed, we now know that there exists various feedback loops between the brain and immune systems that impact signi cantly upon different behavioral processes, including normal behavior and mental disorders. Pioneering efforts in generating this change were initiated by a number of early investigators. Included were those whose efforts were directed at establishing neuroimmune connections as well as others whose research focused upon the relationship between immunity, cytokines, and behavior. This book brings together outstanding scientists and clinicians who have made major contributions to the rapidly developing eld investigating the relationship between immunity and behavior. The book is divided into three parts. The rst part describes pathways by which the brain and immune systems communicate and int- act with each other. In the chapter βCytokines and the BloodβBrain Barrierβ p- vides insight into interactions between the bloodβbrain barrier and cytokines. Such interactions underlie basic communication between the immune system and brain that are present in normal as well as in disease conditions. In the chapter βNeu- chemical and Endocrine Responses to Immune Activation: The Role of Cytokines,β the neurochemical and endocrine consequences of immune challenge and cytokine administration on central neurotransmitter activity are discussed.