The International Energy Agency sponsored this report to provide a review of historical costs, evaluate near-term market trends, review the methods used to estimate long-term cost trajectories, and summarize the range of costs projected for onshore wind energy across an array of forward-looking studies and scenarios. Using three data sets, the report finds that between 1980 and the early 2000s, the levelized cost of energy (LCOE) for onshore wind energy decreased by a factor of three. More recently, LCOE for onshore wind exhibited a steady increase for more than five years but recently decreased again, reaching an all-time low in Europe and the United States. The study also reviews a number of LCOE forecasts through 2030 and based on the 20th-80th percentiles of these forecasts, identifies a possible 20%-30% reduction in the LCOE for onshore wind energy.