The Nansa Valley, in many ways the westernmost drainage basin in Cantabria (N Spain), has traditionally been a blank page in archaeological terms, an area where only a few particular sites were known. The archaeological surveying carried out by the CAEAPgroup, both at cave sites and in the open air, has succeeded in showing that its archaeological record is comparable with that of the central valleys in the region. The results of the study of this record, presented in this book, suggest the existence ofmore or less subtle differences with the eastern part of the region. These divergences vary greatly in the different prehistoric and historic periods. Thus, at some times this valley is seen to form part of a wider area, while at others it displays traits belonging to its own character and appears to be occupied by a single human group. Otherwise, it can be included within the processes of change that affected the rest of the central part of northern Spain, with the diffusion of ideas coming from the south and west, and a powerful influence from the area of the Marina of Cantabria. This volume, a kind of corpus of sites, presents a full catalogue of all known sites in the valley, together with a study of the evolution of human settlement in the area. It is the starting point for future, more detailed, studies examining in depth the cultural adaptations developed by the human groups who lived along this river.