Since 1949, the Food and Agriculture Organization of the United Nations (FAO) and, since the early 1950s, the World Health Organization (WHO) have convened groups of experts to evaluate current scientific knowledge in order to define the energy requirements of humans and propose dietary energy recommendations for populations. The purpose of this information is to assist FAO and WHO in implementing their programmes. The United Nations University (UNU) became part of this joint initiative in 1981. The reports of these expert meetings (see the list of References at the end of this chapter) have become important guidelines on energy in human nutrition for academic scientists, nutritionists, physicians and other health workers, as well as for planners and policy-makers in both the agriculture and health sectors throughout the world.