This chapter addresses the question regarding how seaports may move from a stepwise development to a leadership role in energy transition, as the Port Authority of Rotterdam (the Netherlands) wishes to do. A preliminary framework of conditions that enable a comprehensive shift, given involvement of a petro-chemical complex, is discussed. In Rotterdam’s vision, its new aim does not contradict economic development. Rather, growth is partially created through (niche) pilot projects and experimentation with new, low CO2, energy production and use, and spin-off effects. A crucial factor seems to be support by a national policy of rigorous reduction of CO2 production and emission. Next, the attention shifts to Shanghai (China) and how this port is performing with regard to sustainability changes. Radical shifts such as in Rotterdam seem impossible, however, stringent measures have been taken in Shanghai to increase sustainability in port activities. These measures are discussed and the dilemma of Shanghai is addressed.