Nutrition is a topic of wide interest and importance. In spite of growing understanding of the underlying biochemistry, and health campaigns such as five-a-day, increasing obesity and reported food allergies and eating disorders, as well as the widely advertised supposed benefits of food supplements mean that a clear explanation of the basic principles of a healthy diet are vital. In this Very Short Introduction, David Bender explains the basic elements of food, the balance between energy intake and exercise, the problems of over- and under-nutrition, and raises the question of safety of nutritional supplements.