This chapter discusses the environmental problems of world cities, defines the main priorities of the sustainable agenda and discusses extensively the energy problems of cities in the developed world. The tremendous increase in the population, lack of resources and small or zero development has resulted in poverty and major inequalities. Over-consumption of resources, mainly energy, associated with increased air pollution mainly from motor vehicles, increases in the ambient temperature because of the positive heat balance in cities, heat islands, noise pollution and solid waste management seem to be the more important environmental problems in urban areas of developed countries. Passive and active solar techniques combined with advanced conservation technologies seem to be the most appropriate and efficient solution to this problem. In parallel, energy efficiency and advanced solar energy systems can contribute greatly, in conjunction with other measures, to make urban energy systems in developed countries more sustainable.