Participatory IPM research, through its involvement of farmers, marketing agents, and public agencies, is designed to facilitate diffusion of IPM strategies. However, widespread IPM adoption requires careful attention to a host of factors that can spell the difference between a few hundred farmers adopting IPM locally and millions adopting it over a large area. A number of strategies have been implemented over time in efforts to speed diffusion of IPM around the world. These strategies include working with traditional public extension agencies and approaches and relying on private for-profit and not-for-profit entities that use a variety of specialized training and technology-transfer methods. The complexities of IPM programs; vast differences in local public-extension capabilities; resources, education, and socio-economic differences among farmers; and the need to cost-effectively match IPM strategies to IPM solutions dictates a multi-faceted approach to IPM diffusion if adoption is to be maximized. Given that public resources are scarce, a central issue is how to engage farmers in IPM in a way that maximizes the amount of learning for the resources expended. The purpose of this chapter is to identify some of the lessons learned about how to maximize the depth and breadth o f farmer engagement in IPM.