This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book identifies different types of neurone and discusses nerve impulses, neurotransmitters and types of nerve fibre ending. It looks at the different parts of the brain, and explores the membranes which cover the brain— the meninges—and the cerebrospinal fluid which protects the brain and the spinal cord. The book begins by discussing the function of the central nervous system then also discusses voluntary movement and reflex action. It reviews the history of pain, distinguishes between acute and chronic pain, and examines the modulation of pain. The book considers the mechanisms of Non-steroidal anti-inflammatory drugs, their therapeutic uses and some of the side effects which can be associated with them. It describes the use of opioids: how they work, their pharmacological properties, their effects, their therapeutic use and the problems of tolerance, withdrawal and dependence.