The consumption of natural resources has been increasing continuously during recent decades, due to the growing demand caused by both the economic and the demographic rise of global population. Environmental overloads that endanger the survival of our civilization and the sustainability of current life support systems are caused by the increased consumption of natural resources-particularly water and energy-which are essential for life and for the socio-economic development of societies. While not yet well utilized, process integration and polygeneration are promising tools which reach the double objective of increasing the efficiency of natural resources, and also minimizing the environmental impact. This paper discusses the concepts of polygeneration and energy integration and various examples of polygeneration systems: (i) sugar and energy production in a sugarcane factory; (ii) district heating and cooling with natural gas cogeneration engines and (iii) combined production of water and energy. It is clearly evident that polygeneration systems which include appropriate process integration significantly increase the efficient use of natural resources. (c) 2008 Elsevier Ltd. All rights reserved.