The only way marine current turbines can be connected into the grid meeting some obvious economical and efficiency requirements is being part of a farm.It is then necessary to study, simulate and understand the interactions between marine current turbines when they are exploited in the form of an array. This book tries to clarify how a turbine interacts with the other devices surrounding it. Real physical small scale models of a horizontal axis marine current turbine were designed to behave as similar as possible to a real machine, and an electrical system was designed for the whole assembly to simulate the way a real marine current turbine would be producing energy at a full scale array in a real site, with demand fluctuations and hence different power outputs. The array was tested inside a flume trying different configurations and loading ratios.The performance of the turbines was analyzed focusing on their power output. Wake and blockage effect analysis were also carried out. This analysis should help engineers and researchers trying to achieve a better understanding of this technology, towards a full integration of marine current turbines in the future energy mix.