Increasingly, conventional wisdom dictates that agrarian policy in developing countries should foster a "doubly green revolution" that both protects the environment and boosts output. Like the first green revolution, such a transformation will entail convincing millions of farmers to adopt new practices and, as a result, will confront well-documented barriers to technological change in developing-country agriculture. It will also face a number of new obstacles, including a divergence between the interests of policymakers and farmers, a policy environment biased in favor of input-intensive agriculture, and the fact that many environmentally friendly technologies entail relatively high set-up costs. At least in the short run, institutional constraints will limit the contribution of agricultural biotechnology to overcoming these obstacles. Hence, the first green revolution may serve as an overly optimistic model for a shift to a more sustainable agriculture.