As the role of wind energy grows in the U.S. power grid, there is increased interest and requirements for it to provide 'essential reliability' services (historically often referred to as 'ancillary' services). These services are critical to maintaining the reliability and stability of the grid, and historically were provided by large 'synchronous' generators, mainly fossil-fueled and hydroelectric generators. To help evaluate the potential role of wind in providing these services, this report provides an overview of services provided to the grid, including their technical requirements, quantities currently procured, and some estimates of costs. The report also summarizes the technical and regulatory issues around wind providing these services.