Since 1949, FAO has convened groups of experts to evaluate current scientific knowledge in order to define human energy requirements and propose dietary energy recommendations for populations. The World Health Organization joined this initiative in the early 1960s, followed by the United Nations University in 1981. New scientific knowledge generated during the 20 years since the last consultation prompted the convening of a meeting from 17 to 24 October 2001 at FAO headquarters, Rome to make recommendations for energy requirements of populations throughout the life cycle. This publication is the report of that consultation. The report is not meant merely to describe the energy expenditure and requirements of population groups but is also intended to be prescriptive in supporting and maintaining health and good nutrition, defining human energy requirements and proposing dietary energy recommendations for populations. The publication is accompanied by a CD-ROM containing a software program and an instruction manual on calculating population energy requirements and food needs.