Energy resources, the basic input in every area of the economy, have a fundamental function for society’s welfare. Traditional energy resources are, however, rapidly decreasing. Energy supply has been falling behind in meeting global demand, and is causing increased focus on efficiency and economy concepts in recent energy policies. Since the existing energy resources are not spread evenly among the countries, but instead are concentrated in certain regions and countries, a monopolistic situation arises. Equally, supply assurance is an issue, since the energy supply is held by certain regions and countries who have monopolistic pricing power. Both the EU and many other countries are studying how to marketize energy. This book focuses on the importance of energy and the problems posed by it. It will be useful for the academic community, related sectors and decision makers.