Over the past two decades, the NGO, Practical Action, has implemented a range of food and livelihoods projects with farmers in some of the most marginalised areas of Africa, Latin America and South Asia. A key component of these projects has been the development of local or community-based extension systems (CBES) to bring information, skills and services to farmers and livestock keepers who would otherwise have limited access to government or commercial extension services. This paper looks at policy-related issues surrounding these local extension systems. It identifies the social, economic and technical factors that contribute to the success of CBES, and how local policies and practices have influenced the variety of models of CBES developed and their effectiveness. The paper draws on findings from a study of past projects in Bangladesh, Peru, Sudan and Kenya covering a range of ecosystems and policy environments. It assesses the sustainability of CBES several years after project support has finished, and how CBES can complement government or commercial services. The findings show that these systems do continue to provide a service to farmers after the ending of project support, and that they are valued by the local community. They can also provide more flexible, cost-effective and far-reaching services to resource-poor farmers in marginalised areas than government or commercial extension are able to. As such, recognition and support to CBES should be considered by policy-makers as part of an integrated and pro-poor approach to extension services.