A substancial amount of wind power, 30-60 GW, is foreseen in the northern part of the North Sea. These wind farms have to be connected to the national grids of five different countries in a flexible and economical way. Individual connection is straightforward but for several reasons possibly not the best choice. A high capacity North Sea Transnational Grid connecting wind farms to the national grids and at the same time connecting the national grids may well be a better solution for reasons of energy efficiency, availability, controllability, lower costs and the possibility to trade/exchange electricity.