Networks are commonly used to increase the effectiveness of international agricultural research by involving a number of individuals, organizations or countries in sharing information and other resources. Since its inception, IBPGR has been closely involved in setting up and managing at least 18 plant genetic resources (PGR)-based networks. This paper examines how PGR-based networks can be most effectively established and managed to strengthen the conservation and utilization of plant genetic resources. Four types ·of PGR-based networks are discussed : crop networks, regional networks, base collection networks and topic-based networks. A number of constraints that can reduce a network's effectiveness and a number of important priciples for effective, sustainable networks are examined. Of foremost importance are goals and objectives which are clear, measurable and shared by all network·members. It is concluded that carefully established and managed networks can help to strengthen the conservation and utilization of plant genetic resources.