In the twenty-first century, obesity affects around 20–25% of the population and it is now one of the prime contributors to ill health in modern society. Obesity can cause or exacerbate a variety of health problems and it is often associated with a number of other diseases including type II diabetes mellitus, coronary heart disease and certain types of cancer. The incidence of obesity and related diseases is steadily increasing such that obesity is now regarded as a global epidemic. In recent years, major advances have been made in determining the role of the central nervous system, in particular specific hypothalamic nuclei, in regulating energy balance. From such studies it is apparent that a highly intricate neural system involving a complex interplay between a range of orexigenic and anorectic agents controls food intake and body weight. Thus, a greater understanding of the key neurotransmitter molecules, their related signal transduction pathways and molecular targets, as well as the neuronal pathways that control release of these neurotransmitters is vital if novel therapeutic targets for the treatment of obesity and related diseases are to be uncovered. This book provides a concise overview of recent developments in this field. As an introduction, Professor Bloom gives an outline of the factors that are known to play a key role in regulating energy balance and the development of obesity in humans.