Wind power systems are susceptible to shear in the free-stream wind. While past work in wind power systems has focused on assessing shear in wind speed, work from other disciplines has shown the existence of shear in wind direction, most often in the stable nocturnal boundary layer. Preliminary tall tower observations from Lubbock, Texas show this relationship as well. Potential meteorological causes for these phenomena are given, along with an introduction to the aerodynamic problem that arises in the presence of directional shear. The aerodynamic problem of direction shear is shown to be different from the case of turbine operation in yawed flow, and future work is outlined to quantify its impact on wind power systems.