Energy is a key theme for future world development. Worldwide energy demand is mounting rapidly, particularly in the developing and newly industrialising countries, which seek to catch up with the level of economic development attained by industrialised countries. The great challenge now is to meet this energy demand in a sustainable manner. However, sustainable development will be inconceivable without a deep-seated reconfiguration of worldwide energy systems. One goal in this context must be to protect natural life-support systems and, in particular, to prevent dangerous anthropogenic perturbation of the climate system. If the present path continues and rising energy demand is met mainly from fossil sources, this would trigger intolerable global climate change with high consequential costs, and would thus also jeopardize economic development. A second necessary goal is to eradicate energy poverty in developing countries in order that these countries can make use of development opportunities. It is essential that 2.4 billion people gain access to modern forms of energy so that they can shake off the yoke of energy poverty. To attain these two goals, energy systems need to be turned towards sustainability. To that end, efficiency must be improved at all levels of the energy system, and fossil energy sources must be substituted by renewable ones. The potential of renewable energies, above all solar energy, is almost unlimited and can be harnessed sustainably. Energy system transformation towards sustainability is thus the first step into the solar age. However, without rapid and resolute international policy support, the expansion of renewable energy sources will not be able to develop the necessary dynamics in time. The International Conference for Renewable Energies (renewables 2004) held in Bonn 2004 is a milestone for this process.