We investigate the influence of future land development on current agricultural land values. From a theoretical model of land markets, we derive a reduced-form expression for agricultural land values in terms of observable variables. This result dictates the specification of our econometric model and we find strong support for the model in an application to New York State. The estimated model, together with a spatial interpolation algorithm, is used to generate a surface of estimated development rights values for Orange County. This approach overcomes several problems that arise with the use of standard appraisal methods to value conservation easements.