This paper presents an overview of current opportunities and challenges facing efforts to increase the impact of rural and agricultural extension. The starting point for this analysis is in recognition that the days when agricultural extension was synonymous with the work of public sector agencies are over. The ‘extension services’ described here may just as likely consist of an input vendor advising a farmer about what seed to plant, a television station broadcasting a weather forecast, a supermarket advising traders about what standards are required for the vegetables they purchase or a farmer organization lobbying for research that refl ects the demands of its members for new technologies. Mobilizing the potential of extension is about enhancing this broad and complex fl ow of information and advice in the agrifood sector. The ideas presented here describe how extension systems can contribute to the improvement of the profi tability, sustainability and equity of smallholder agriculture within broader innovation systems. This paper outlines the potential role of extension in achieving the aims of the L’Aquila Food Security Initiative, which has mobilized a massive international commitment to enhancing food security. Effective extension systems are a precondition but not a guarantee that these aims can be achieved. Extension will only be effective if other services are in place, if research is focused on the problems facing farmers, if markets and land are accessible and if there is suffi cient social, political and economic security in place to create an enabling environment for rural development. Extension is part of agricultural knowledge and information systems, which are in turn part of the agrifood and rural development innovation systems that frame the prospects for rural poverty alleviation and food security. Extension has a crucial contribution to make to these broader systems