The main goal of this paper is to outline characteristics and critical aspects related to the design and operation of offshore and subsea electric distribution grids, particularly in the case of high penetration of distributed and intermittent renewable energy sources. At first, the paper provides an overview of electric loads operating in the ocean environment, surveys their power and energy demands and presents their main operational characteristics and corresponding maturity of technology. Subsequently, the potential of marine renewable energy sources is identified by analyzing their degree of development, typical power range and suitability to supply the offshore loads. Based on an up-to-date review of previous studies and real test cases, this paper shows how conditions to enable the development of “offshore smart grids” can be met and it outlines emerging trends in the electrification of the ocean space.