On January 12 2010, Haiti was hit by an earthquake of 7.2 on the Richter scale. Close to 220,000 persons died, more than 300,000 were wounded and almost two other million were displaced. The earthquake¿s epicenter was actually several kilometers away the capital, in the city of Léogâne, approximately 80% of which was destroyed. Three other medium-sized cities ¿ Grand-Goâve, Petit-Goâve and Jacmel - were also deeply affected by the earthquake. These four cities were the field of study for this thesis, which argues that this type of event, a natural disaster, triggers a crisis. The main hypothesis is that the crisis catalyzes tensions, reveals structures and can be a factor of transformation in the governance of medium-sized cities, which has long been ignored by both academia and government. Approaching the crisis in terms of crisologie (Morin, 1976), proved to be the best way of identifying January 12th as an event and the starting point of a crisis, of distinguishing its causes from its consequences and of understanding the processes at work. Urban governance in Haiti was analyzed at three specific levels (systemic, cybernetic and neguentropic). Antagonisms characteristic of crises appeared at each level. Then, considering the city as ¿ordinary¿ refocus the debate on small and medium-sized cities of the South and was a way to use intermediation as an analytical tool to reveal the structures of urban governance. Eight intermediation dimensions were created for and applied to each of the cities studied. This tool both reveals a spatial typology of these cities (influenced, satellite or remote from a metropolis) and serves as a basis for the surveys on representations that were conducted among local stakeholders. These surveys help link intermediation with the ¿shared urbanity¿ of these cities, indicating how urbanity, autochthony and the reputation given to each city from outside function as elements that force inhabitants to position themselves on the national urban scene. Several important findings emerged through the study of governance in times of emergency and of reconstruction, both at the national and local levels, and through urban development projects in the cities being studied, highlighting their governance trajectories. The urban functions of the cities revealed that their spatial typology combined with their shared urbanity influence the intervention of international actors in their territories and impacts on the governance mechanisms between local, national and international stakeholders.This research highlighted also the importance of political factors which create confusion between political boundaries, resulting in an absence of differentiation between local and national powers within Haitian society. The particularities of the local contexts show too that society¿s participation strongly depends on local urban governance. Initiated only by international actors, it can lead to relative inefficiency, or even counter-productivity, if it is not socially engineered to the technicality of the projects. Finally, this work allowed to discuss the pertinence of two normative prerequisites that guide international community¿s intervention in developing countries: the criteria of good governance and the concept of fragile, bankrupt, failing or collapsed State, both centrals nowadays in the attribution of public development aid.