Reunion island, a French Department in the Indian Ocean, is densely populated, with 653600inhabitants in a confined area of 2512km2, which gives a density of 260 inhabitants per square kilometre. About 65% of its population can be considered as urban. However, about ten only of the eighty five built-up areas counted on the island really appears as towns. They are all on the littoral but present very inequal levels of development. These characteristics find their explanation in Reunion's political and economic history. The paper first examines the level of urbanization in Reunion Island today, by giving in particular a definition of the notion of town in the insular context; then, it goes through the main factors which have influenced the urban process from settlement to the present day and it ends with an analysis of the urban forms resulting from the evolution and which can be placed in two prevailing models.