The scope of intellectual property rights (IPRs) has been expanded in recent years to cover plant varieties. Plant breeders' rights (PBRs) provide weak protection to private plant breeders in many countries. The United States and a few other developed countries provide patent protection to plant varieties as well as to some genetic resources. In principle, the strengthening of IPRs for plants should encourage more plant breeding and more variety options for farmers. However, developing countries often lack the institutional setting to enable them to realize these options. A second type of IPR providing for “farmers' rights” has been prepared in the Convention on Biodiversity. Negotiating a payment framework for farmers' rights may result in a period of limited international exchange of genetic resources. Policy simulations based on an international economic model confirm that developing countries will be harmed by weak IPRs while developed countries will not be affected. They also confirm that both developing and developed countries will be harmed by reduced exchange of genetic resources associated with protracted negotiations over farmers' rights.