The history of death is entangled with the history of changing social values, meaning that a shift in attitudes to death will be consistent with changes in a society’s world view. Late Mesolithic shell middens in the Tagus and Sado valleys, Portugal, constitute some of the largest and earliest burial grounds known, arranged and maintained by people with a hunting, fishing, and foraging lifestyle, c 6000–5000 cal BCE. These sites have been interpreted in the light of economic and environmental processes as territorial claims to establish control over limited resources. This approach does not explain the significance of the frequent disposal of the dead in neighbouring burial grounds, and how these places were meaningful and socially recognized. The aim of this dissertation is to answer these questions through the detailed analysis of museum collections of human burials from these sites, excavated between the late nineteenth century and the 1960s. I examine the burial activity of the last hunter-gatherers of the south-western Iberian Peninsula from an archaeological perspective, and explain the burial phenomenon through the lens of historical and humanist approaches to death and hunter-gatherers, on the basis of theoretical concepts of social memory, place, mortuary ritual practice, and historical processes. Human burials are investigated in terms of time and practice based on the application of three methods: radiocarbon dating and Bayesian analysis to define the chronological framework of the burial activity at each site and valley; stable isotope analysis of carbon and nitrogen aimed at defining the burial populations by the identification of dietary choices; and archaeothanatology to reconstruct and define central practices in the treatment of the dead. This dissertation provides new perspectives on the role and relevance of the shell middens in the Tagus and Sado valleys. Hunter-gatherers frequenting these sites were bound by shared social practices, which included the formation and maintenance of burial grounds, as a primary means of history making. Death rituals played a central role in the life of these hunter-gatherers in developing a sense of community, as well as maintaining social ties in both life and death.