The intensity of tidal currents can be accurately predicted far in advance. This also makes them an attractive renewable maritime energy source. Tides are very long waves that occur twice a day and set a large amount of water in motion. High current speeds can occur when the water enters certain confined areas. With the help of tidal turbines, kinetic energy can be generated from the tidal current. This drives the rotor of the tidal turbines, which can be mounted on a foundation or floating structure. Since the density of water is more than 800 times higher than that of air, the diameter of a turbine rotor is much smaller than the one of a wind turbine rotor. Currently, there is no single solution for the best method of harvesting wave energy, but in recent years a number of promising concepts have been presented for further development. Tidal turbines can be an attractive solution for coastal locations that are not connected to the public grid due to their small size or location, such as small islands.