In the United States, there has been substantial recent growth in wind energy generating capacity, with growth averaging 24% annually during the past five years. With this growth, an increasing number of states are experiencing investment in wind energy. Wind installations currently exist in about half of all U.S. states. This paper explores the policies and market factors that have been driving utility-scale wind energy development in the United States, particularly in the states that have achieved a substantial amount of wind energy investment in recent years. Although there are federal policies and overarching market issues that are encouraging investment nationally, much of the recent activity has resulted from state-level policies or localized market drivers. In this paper, we identify the key policies, incentives, regulations, and markets affecting development, and draw lessons from the experience of leading states that may be transferable to other states or regions. We provide detailed discussions of the drivers for wind development in a dozen leading states-California, Colorado, Iowa, Kansas, Minnesota, New York, Oregon, Pennsylvania, Texas, Washington, West Virginia, and Wyoming.