Modern wind farms typically comprise a large number of wind turbines spread on a relatively small area. The closely spaced turbines are aerodynamically coupled since they share the common energy resource. The aerodynamical coupling is described by the wake model, which explains how the change in the energy extraction of a single wind turbine affects the operating conditions of other turbines. Wake models provide the basis for optimization of wind farm operation. The paper shows that at wind speeds lower than rated the wind farm power production can be increased by optimizing the rotor speed of individual wind turbines. Furthermore, at wind speeds above rated the power production can be redistributed among the turbines in the wind farm in order to equalize the loads and thus prevent excessive wear and tear of the exposed turbines.