This paper will present a review of the use of Air coupled ultrasonics for nondestructive evaluation of wind turbine blades carried out at the CNDE, Iowa State University. Results will show the use of air coupled ultrasonics to scan thick composite sections of 40m wind turbine blades including the spar cap, the leading and trailing edges. Detection of defects such as slots, holes, fiber waviness (both in-plane and out-of-plane waviness), delaminations and dry fibers will be presented. Other features like adhesive thickness and length estimation in spar cap/shear web section and the trailing edge section will also be presented. The use of air coupled UT is not limited to just detection, but also characterization of the detected defects. Results highlighting the use of ultrasonic velocity to characterize defects will be presented. This includes defining damage index in terms of velocity, as well as development of stiffness maps to show reduction in structural stiffness based on the defect. Additionally, the challenges of NDT of wind turbine blades using conventional ultrasonics will also be presented.