La vulnérabilité alimentaire d'un individu peut être définie comme la susceptibilité qu'il a de faire face, à plus ou moins longue échéance, à une situation d'insécurité alimentaire, au cours de laquelle il n'a plus accès à une nourriture suffisante et satisfaisante d'un point de vue nutritionnelle et sanitaire, et correspondant à ses préférences culturelles. l'enjeu de la thèse est de comprendre les facteurs qui déterminent le niveau de vulnérabilité alimentaire des citadins – puisqu'on s'intéressera au cadre urbain. les citadins élaborent des stratégies de gestion des ressources qu'ils peuvent mobiliser pour faire face aux changements de l'environnement dans lequel ils vivent ; ils s'inscrivent dans le système alimentaire urbain et élaborent des choix de vie (migrations, emploi, logement, investissements) qui tracent une trajectoire de vie, dont leur situation alimentaire dépend. l'enjeu de la thèse est de comprendre ce qui, dans la position que l'individu occupe au sein de son environnement, accroît ou réduit sa vulnérabilité. le terrain d'étude sera la ville de hanoi, capitale du viêt-nam, dont une partie des habitants souffre d'une situation précaire, les conduisant, en cas de choc, à ne plus pouvoir faire face et à se retrouver en insécurité alimentaire. / With a focus on underpriviledged urban dwellers’ everyday practices in Hanoi, this study aims to show the construction of individual and household food insecurity in a city where living standards have dramatically improved over the last three decades. It demonstrates that food budget plays a key role in livelihoods management in an unstable context, by serving as a tool for underprivileged people to adjust to shocks. Therefore, individuals’ food vulnerability should be understood as a long-term livelihoods securitization process.This study shows that livelihoods securitization is based on sustaining social networks. These networks are constantly reactivated by an ongoing circulation of money and goods, and they are the basis of daily mutual assistance at the ward scale. This reveals a strong relationship between lived space and solidarity networks in which risks are mutualized.The analysis of people’s working trajectories shows a high capacity for adaptation, with individuals rearranging their livelihoods (jobs, food production for family’s consumption, rental income, etc.) according to their need and the changes in their environment. Nevertheless, in the context of a metropolizing city, the people’s capacities to take advantage of this development varies greatly. This contrast is reinforced by the fact that resources developments (economic, social, spatial) have a cumulative effect. As a consequence, inequalities are deepened in Hanoi, both at the city scale and wards scale.Such inequalities can be seen in the increasing differences between food practices and consumption patterns among urban dwellers. Products as well as their origines get more diverse, creating new safety concerns ; purchasing places diverge more and more between the rich and the poor ; and foodborne diseases appear while malnutrition issues remain. All along the food supply chain, current shifts illustrate a process that can be called food emergence.Finally, this study reveals that it is primarily non-food phenomenons that result in food insecurity ; it widens the food security framework. In this way, the analysis of urban dwellers’ daily practices provides an illustration of the ongoing urban emergence process of Vietnamese capital.