Open-air rock-art forms one of the most widely distributed categories of prehistoric culture with examples recognized across the Old and New Worlds. It is also one of the most threatened features of human heritage and is susceptible to accelerated decay as a result of natural processes. Considering the specific case of the Coa Valley rock-art complex in Portugal, but also analysing case studies originating from other countries (Norway, Brazil, Southern USA and South Korea), this richly illustrated book addresses open-air rock-art natural degradation causes, suitable methods to assess current condition and the creation of urgency scales for conservation interventions.