The wind power deployment and realization requires an accurate wind power assessment at the site of interest. As a rule of thumb, one should have at least one year wind speed and direction measurements at different heights. A small error in wind speed measurements causes an error of power three in the wind power density estimation. The wind speed and direction sensors which are commonly used and are recommended are mechanical in nature. These sensors are expected to loose accuracy with time due to mechanical malfunctioning, dust penetration in to the moving parts, dust accumulation on the anemometer cups, icing and other environmental effects. Hence it is necessary to study the effect of the tower on wind speed measurements. This can be achieved by installing two sensors at different height. The present book put an emphasis on that.