The aerodynamic subsystem is essential for the operation of a wind turbine but at the same time probably the most difficult to model in a satisfactory way. On the one hand, it has very fast dynamics such that it is possible to assume steady-state algebraic equations and, on the other hand, these equations include much heuristics and are unprecise. The reality shows that the dynamics is spatially distributed and unsteady. Hence, the use of computational fluid dynamics calculations (CFD) is the state of the art for the study of wind but is inadequate for control. The present chapter introduces the subject attempting a presentation without losing the control application perspective.