This fourth edition of The State of Food Insecurity in the World (SOFI) provides the latest estimates of the number of chronically hungry people in the world and reports on global and national efforts to reach the goal set by the World Food Summit (WFS) in 1996 to reduce that number to half the level reported at the time of the Summit by the year 2015. The report is divided into four main sections. The first section, Undernourishment around the world, analyses the latest data on hunger. Other articles combine this data with other indicators to chart the fatal connection between hunger and mortality and the strategic connection between combating hunger and achieving the Millennium Development Goals. The second section contains a special feature on mountain people and mountain environments. This presents preliminary results from a multidisciplinary study carried out as part of FAO's contribution to the International Year of Mountains. The study used newly available georeferenced data to estimate the number of mountain people vulnerable to food insecurity. In the third section, Towards the Summit commitments, a series of articles discusses approaches to fulfilling the commitments in the WFS Plan of Action. Finally, as in every edition of SOFI, two sets of tables provide detailed information on the prevalence in developing countries and countries in transition of under nourishment and on food availability, dietary diversification, poverty, health and child nutritional status. SOFI draws on the ongoing work of FAO and its international partners in monitoring the nutritional status and analysing the vulnerability of populations worldwide. It represents part of FAO's contribution to the Inter-Agency Food Insecurity and Vulnerability Information and Mapping Systems initiative.