Using data from villages in three districts of Western Rajasthan, this paper describes the decline in area and deterioration in quality of common property resources over three decades. The decline of common property resources is associated with institutional changes in the villages. The introduction of land reforms in the early 1950s led to large-scale privatization of common property resources, reduced the private cost of use of common property resources, and slackened their upkeep by disrupting the traditional management system. Increased commercialization of livestock farming, increased use of tractors, and demographic pressure also played roles in the process. Farmers adjusted to shrinking common property resources by reducing herd size, by changing its composition, and by relying more on private resources to rear animals. These changes tend to reduce the comparative advantage of livestock farming in the arid region. Since the shrinkage of common property resources is largely a result of the transfer of submarginal lands from grazing to cropping, resource degradation is accelerated.