Around 9500 BC, a number of changes take place in the life ways of human groups that, henceforth, will be designated as Mesolithic. These changes set them apart, behaviourally, from the preceding periods. Even though the ancestral know-how was passed across the Pleistocene/Holocene boundary, new solutions were implemented. Groups became more mobile and more dependent on the exploitation of marine resources. Shell middens crop up not just all along the Atlantic façade but also in more interiorly located sites. Technical choice and mode of resource extraction are situationally adapted and/or created. This behavioural flexibility is specific to the early Mesolithic and contrasts with the rigidity of Magdalenian peoples’ technical systems. The History of the earliest Mesolithic communities in Portugal is mainly based on the study of three key-early Mesolithic sites, Toledo, Areeiro III and Barca do Xerez de Baixo, with a main focus on their lithic industries (recreating all the production process), although other archaeological components are also presented and discussed. Despite being contemporary on a radiocarbon scale (they all accumulated during the Boreal chronozone), each of these sites represents a distinct way of using space and the available local resources.