Clean energy and energy supply have become a concern worldwide, for energy itself is deemed a strategic trading commodity. This book explores whether the consideration of cross-border interconnection of transmission grids at a large-scale along with unrestrained legally-secured power transit might play a significant role in solving such a concern whilst contributing to achieve sustainable development. This book addresses the question of what international legal mechanisms could be employed to remove barriers hindering cross-border grid interconnections, thus facilitating power-trade and transit as well as to take advantage of opportunities for energy efficiency capable to secure 'green' energy supply, reduce atmospheric emissions and, ultimately, targeting sustainable development, at least, in regional contexts. The author advances the proposition that cross-border power grid interconnection coupled with an international legal framework realigned to harmonise energy mixes may solve the concerns on clean energy and energy security by contributing to the integration of renewable energy technologies at a large-scale and promoting unrestrained power flow and trade across-borders.