Ocean and tidal currents offer the possibility of generating energy regularly and, above all, constantly. It offers the advantage of a higher energy density compared to many other renewable energy sources. The potential of ocean energy as a resource is immense and concentrated in several locations around the world. The second part of this paper provides an overview of the general differences between ocean current and tidal current. The third part outlines different types of construction for the extraction of the water's kinetic energy, taking into account environmental influences and technical difficulties. In addition, this chapter reviews the operation of such plants in extreme situations and the connection to the local power grid. The next part discusses the rough procedure for developing the rotor geometry while Chapter 5 explores existing projects. Finally, the next step presents a possible real-world application assessing the feasibility of a project located at the strait of Gibraltar. This chapter discusses the various design aspects and presents a financing concept. The last chapter gives an conclusion.