During the Late Iron Age two processes developed in Iberia: a process of growing demography and a trend towards nucleated settlements. Both processes ended in the appearance of large fortified settlements (oppida), well known through archaeology and written sources. As in other areas of Europe, there were probably substantial differences between settlements, in terms of geographical setting, size, form, and function. In the end, the first cases of urbanization at the end of the Iron Age are presented as changing and multi-faceted entities in space and time, with similarities and unique characteristics. We discuss this process and the insights we can glean from it. Two worlds, the Mediterranean in the east and south and the Atlantic in north and west, had contacts through inland territories and navigations. The exploration of the relationships between oppida, demography, social organization, and urbanization is considered in this paper.