Windy Gap is the most recent major transmountain water diversion project constructed in the State of Colorado. It diverts water from the Colorado River Basin eastward across the continental divide to the Front Range and East Slope. The idea for Windy Gap developed out of a 1950s U.S. Bureau of Reclamation report on the Colorado-Big Thompson Project, but it was not until the 1960s that construction of Windy Gap was seriously considered. By late in the decade, however, major water development projects were being increasingly questioned and criticized. Environmental statutes and regulations combined with historic West Slope opposition to transmountain water diversion in Colorado led to lengthy delays for Windy Gap. The purpose of this report is to examine some of the issues surrounding the practice of transmountain water diversion and to place Windy Gap in that context.