The yaw system of wind turbines is the component responsible for the orientation of the wind turbine rotor towards the wind.

The task of orienting the rotor into the wind was a complicated issue already for historical windmills. The first windmills able to rotate in order to "face" the wind appeared in the mid-18th century. Their rotatable nacelles were mounted on the main structure of the windmill using primitive wooden gliding bearings lubricated with animal fat. The necessary yawing torque was created by means of animal power, human power or even wind power (implementation of an auxiliary rotor known as fantail).

Vertical-axis wind turbines (VAWTs) do not need a yaw system since their vertical rotors can face the wind from any direction and only their self rotation gives the blades a clear direction of the air flow. Horizontal-axis wind turbines (HAWTs), however, need to orient their rotors into and out of the wind and they achieve that by means of passive or active yaw systems.

HAWTs employ some sort of yaw system which can be passive or active. Both passive and active systems have advantages and disadvantages and various design solutions (both active and passive) are being tried in order to find the optimal design for each wind turbine depending on its size, cost and purpose of operation.

The active yaw systems are equipped with some sort of torque producing device able to rotate the nacelle of the wind turbine against the stationary tower based on automatic signals from wind direction sensors or manual actuation (control system override). The active yaw systems are considered to be the state of the art for all the modern medium and large sized wind turbines, with a few exceptions proving the rule (e.g. Vergnet). The various components of the modern active yaw systems vary depending on the design characteristics but all the active yaw systems include a means of rotatable connection between nacelle and tower (yaw bearing), a means of active variation of the rotor orientation (i.e. yaw drive), a means of restricting the rotation of the nacelle (yaw brake) and a control system which processes the signals from wind direction sensors (e.g. wind vanes) and gives the proper commands to the actuating mechanisms.

The most common types of active yaw systems are:

The passive yaw systems utilize the wind force in order to adjust the orientation of the wind turbine rotor into the wind. In their simplest form these system comprise a simple roller bearing connection between the tower and the nacelle and a tail fin mounted on the nacelle and designed in such a way that it turns the wind turbine rotor into the wind by exerting a "corrective" torque to the nacelle. Therefore, the power of the wind is responsible for the rotor rotation and the nacelle orientation. Alternatively in case of downwind turbines the tail fin is not necessary since the rotor itself is able to yaw the nacelle into the wind. In the event of skew winds the "wind pressure" on the swept area causes a yawing moment around the tower axis (z-axis) which orients the rotor.

The tail fin (or wind vane) is commonly used for small wind turbines since it offers a low cost and reliable solution. It is however unable to cope with the high moments required to yaw the nacelle of a large wind turbine.^{[citation needed]} The self-orientation of the downwind turbine rotors however is a concept able to function even for larger wind turbines. The French wind turbine manufacturer Vergnet has several medium and large self-orienting downwind wind turbines in production.