The extensive work presented here takes a new look at the prehistoric art preserved on various megalithic monuments from the northwestern Iberian Peninsular. The initial chapters (1-3) deal with the objectives of the study, the history of research of megalithic art in the Iberian Peninsula, and the discussion on the area of study. In chapter 4, the research methodologies applied are described in detail: fieldwork (identification, cataloguing and diagnosis), the analysis of stone and paint samples (including radiocarbon dating), and the systems used for the recording of the images. In chapter 5, the most extensive of the book, each of the megalithic sites studied is described, with special emphasis on the description and recording of megalithic art, its state of preservation and the need for conservation actions that would stop its degradation. Chapter 6 deals with the information obtained on this kind of megalithic art. Chapters 7 and 8 deal with the degradation processes and the proposal for preservation measures, not only for the prehistoric art itself, but also for the megalithic sites. Chapter 9 contains the discussion on the main findings.