Natural lands provide irreplaceable ecosystem services, such as wildlife habitat, water filtration and carbon sequestration, but in many regions, they are rapidly being converted to agricultural or urban uses. To counteract this trend, numerous land conservation programs purchase natural land but the impact of these programs is almost entirely unknown. This dissertation develops a framework for evaluating the impact of land conservation programs that incorporates theory from land economics and conservation planning. It posits that private land that enrolls in these programs will have lower economic value and higher ecological value than unenrolled lands. To test the framework, a Propensity Score Analysis is conducted for a federal conservation easement program in the northern plains of the United States. Measures of key economic characteristics (such as a tract's soil productivity, slope and distance to grain markets) and key ecological characteristics (such as a tract's accessibility to nesting pairs of migratory birds and the extent of grassland coverage surrounding a tract) are computed in a Geographic Information System. These measures are used to estimate a logistic regression model that predicts the probability that a tract of land enrolled in the program between 1990 and 2001. Consistent with expectations, tracts with lower economic value and with higher ecological value were more likely to enroll in the program. Using the predicted values from this model, enrolled tracts were matched with control tracts using four specifications of nearest neighbor matching with calipers. Under each of these specifications, the rate of grassland conversion between 2001 and 2006 on enrolled tracts was significantly lower (p<.0001) than the rate of conversion on control tracts by between 0.32 percent (for the specification with the lowest estimate) and 0.42 percent (for the specification with the highest estimate). These results indicate that the program did have a statistically significant impact on the rate of grassland conversion during this time period, although the impact was substantively slight.