The size of wind turbines has been increasing steadily over the past decades, and the majority of these turbines are built in wind farms. As downstream turbines will be operating in the turbulent wakes of the upstream turbines, it becomes more and more important to understand the turbulence evolution mechanisms within the wake of a wind turbine for improved load calculations, wind farm layout optimization, and wind farm control methods. In this chapter, the evolution of turbulence within the wake of a single turbine exposed to uniform and atmospheric boundary layer inflow is therefore discussed in detail with views on velocity components, turbulence intensity, length scales, Reynolds stress, energy spectra, and intermittency. Approaches to include turbulence in wake models are explained. Further, turbulence in wakes of yawed turbines will briefly be commented on, and a comparison of turbulence generated by an actuator disk and a wind turbine will be given since the actuator disk concept is an established concept to simplify simulations and experiments.