In the summer of 2003, when millions of people in the northeastern USA and later in Italy were cut off from power for hours, a topic suddenly came back into intense discussion in Europe: supply security. Until then, economic and especially ecological aspects of energy supply had been the focus for a long time. This changed perspective is also influenced by the liberalization of European electricity markets, which leads to significant changes and consequently to uncertainty among market participants. The content of this book addresses exactly this issue: the originally designed interconnected system for regional power supply and mutual assistance is reaching its limits due to increasing international electricity transport. Limited transmission capacities between national power grids lead to bottlenecks, which pose an obstacle.