This study analyzes the potential impact of state tax incentives on the federal production tax credit (PTC) for large-scale wind power projects. While the federal PTC provides critical support to wind plants in the U.S., its so-called 'double-dipping' provisions may also diminish the value of - or make ineffectual - certain types of state wind power incentives. In particular, if structured the wrong way, state assistance programs will undercut the value of the federal PTC to wind plant owners. It is therefore critical to determine which state incentives reduce the federal PTC, and the magnitude of this reduction. Such knowledge will help states determine which wind power incentives can be the most effective.