IntechOpen is the world's leading publisher of Open Access books, built by scientists for scientists. With 7,400 Open Access books available, 193,000 international authors and editors, and 210 million downloads, IntechOpen delivers content to 154 countries. Its authors are among the top 1% most cited scientists, with 14% contributors from top 500 universities. Books are indexed in the Web of Science™ Book Citation Index (BKCI). The chapter discusses the aerodynamics of wind turbines, focusing on steady-state operation. It covers the analysis of horizontal axis wind turbines (HAWTs), starting with the actuator disc model, which simplifies the turbine as a disc with pressure drop across it. This model helps understand overall turbine efficiency but not blade design. More advanced methods like momentum theory, blade element theory, and blade element momentum (BEM) theory are introduced. BEM theory combines momentum and blade-element theories to determine blade shape and rotor performance under ideal conditions. The actuator disc model assumes no friction, homogeneous, incompressible, steady-state flow, and constant pressure. The analysis involves mass and momentum conservation, leading to equations for power output and thrust. The axial induction factor (α) and rotational induction factor (α') are defined, and equations for power coefficient (Cp), thrust coefficient (Ct), and tip-speed ratio (λ) are derived. The rotating annular stream tube analysis extends the actuator disc model to include rotational effects, considering angular momentum and torque. Equations for wake velocities and pressure differences are derived, leading to expressions for power and thrust. The analysis accounts for rotational motion, leading to more accurate predictions of rotor performance. Blade element theory divides the blade into elements, considering lift and drag forces based on airfoil characteristics. The blade element momentum (BEM) theory combines blade element and momentum theories to determine blade performance. Equations for lift and drag coefficients are used to calculate forces on each blade element, leading to expressions for torque and thrust. Tip losses are considered in BEM theory, with a correction factor (f) accounting for reduced forces at the blade tips. The tip-loss factor is derived from Prandtl's equation, adjusting the power coefficient for tip losses. Blade design involves determining geometric parameters (chord length, twist angle) for optimal performance. The design process uses the BEM theory, considering the optimal relative wind angle and tip-speed ratio. The blade is divided into elements, and local parameters are calculated for each element. The chapter concludes by emphasizing the importance of aerodynamic design in wind turbine performance, highlighting the iterative process of optimizing rotor geometry. The BEM method is widely used in wind turbine design due to its simplicity and accuracy in performance prediction. However, it has limitations in accurately estimating wake effects and complex flows. The chapter provides a comprehensive overview of wind turbine aerodynamics,IntechOpen is the world's leading publisher of Open Access books, built by scientists for scientists. With 7,400 Open Access books available, 193,000 international authors and editors, and 210 million downloads, IntechOpen delivers content to 154 countries. Its authors are among the top 1% most cited scientists, with 14% contributors from top 500 universities. Books are indexed in the Web of Science™ Book Citation Index (BKCI). The chapter discusses the aerodynamics of wind turbines, focusing on steady-state operation. It covers the analysis of horizontal axis wind turbines (HAWTs), starting with the actuator disc model, which simplifies the turbine as a disc with pressure drop across it. This model helps understand overall turbine efficiency but not blade design. More advanced methods like momentum theory, blade element theory, and blade element momentum (BEM) theory are introduced. BEM theory combines momentum and blade-element theories to determine blade shape and rotor performance under ideal conditions. The actuator disc model assumes no friction, homogeneous, incompressible, steady-state flow, and constant pressure. The analysis involves mass and momentum conservation, leading to equations for power output and thrust. The axial induction factor (α) and rotational induction factor (α') are defined, and equations for power coefficient (Cp), thrust coefficient (Ct), and tip-speed ratio (λ) are derived. The rotating annular stream tube analysis extends the actuator disc model to include rotational effects, considering angular momentum and torque. Equations for wake velocities and pressure differences are derived, leading to expressions for power and thrust. The analysis accounts for rotational motion, leading to more accurate predictions of rotor performance. Blade element theory divides the blade into elements, considering lift and drag forces based on airfoil characteristics. The blade element momentum (BEM) theory combines blade element and momentum theories to determine blade performance. Equations for lift and drag coefficients are used to calculate forces on each blade element, leading to expressions for torque and thrust. Tip losses are considered in BEM theory, with a correction factor (f) accounting for reduced forces at the blade tips. The tip-loss factor is derived from Prandtl's equation, adjusting the power coefficient for tip losses. Blade design involves determining geometric parameters (chord length, twist angle) for optimal performance. The design process uses the BEM theory, considering the optimal relative wind angle and tip-speed ratio. The blade is divided into elements, and local parameters are calculated for each element. The chapter concludes by emphasizing the importance of aerodynamic design in wind turbine performance, highlighting the iterative process of optimizing rotor geometry. The BEM method is widely used in wind turbine design due to its simplicity and accuracy in performance prediction. However, it has limitations in accurately estimating wake effects and complex flows. The chapter provides a comprehensive overview of wind turbine aerodynamics,