Recent food riots brought home the crucial importance of food and agriculture in dramatic fashion. They are one of this century¿s major concerns. Beyond the current crisis, world agriculture must address three challenges: demographic growth - we will be 9 billion people in 2050 - and food security in both quantity and quality; protection of the environment and natural resources; and the growing scarcity of fossil fuels. In this perspective, we decided in early 2006 to take the initiative of developing a capacity to analyse the possible balances of global food and agricultural systems in 2050. This document summarises some of the results of this "Agrimonde" foresight study. We have a twofold objective: to provide our two institutions, and more generally our country, with a basis for discussion of global food and agriculture issues, and to identify the top priority research questions submitted to CIRAD and INRA and to international agricultural research as a whole. The challenge of food forces us to understand and plan ahead, and to carry out research through debated priorities.