Wind energy is regarded as one of the most appealing and rapidly expanding energy sources worldwide. The wind energy is converted to power using wind turbines. In this chapter, an overview of the wind energy is introduced and discussed. Then, the classifications of the wind turbines are presented, including vertical and horizontal axis wind turbines. Besides, the main governing equations that determine the turbine’s performance are presented. Also, the wind turbines’ characteristics and design features are introduced. Finally, more details on the wind farms are discussed. The wind turbines are classified into vertical axis and horizontal axis wind turbines. The wind turbine systems scales are classified into small scale that generates less than 100 kW, medium scale of power production ranging between 100 kW to 1 MW, and large scale producing power more than 10 MW. Wind farms are classified into onshore wind farm and offshore wind farm.