In this paper I discuss the relationship between archaeology and historical linguistics, and present a case study from my own research on the diffusion of the Southern Jê languages. For a long time, archaeologists were not aware of the fact that the Kaingang and Xokleng languages were related to the Jê languages of Central Brazil, and proposed an autochthonous origin for those southern groups. A new generation of archaeologists, aware of the relationship between Kaingang and Xokleng and the Jê language family, focused on the identification of their migration. The emergence of the so called Taquara-Itararé archaeological tradition around AD 220 was thought to signal the arrival of Jê speakers to the south. In my research I analyzed assemblages of Taquara-Itararé pottery from different areas of Southern Brazil, combined with the available radio-carbon dates, and with the most recent data on subsistence. The chronological and cultural frame resulting from these data corroborates previous hypotheses that the appearance of pottery coincides with a process of population growth fostered by intensive Araucaria pine nut exploitation and maize-tuber agriculture, which rapidly led to the filling up of the landscape by these new settlers and to territorial circumscription—the formation of more restricted and territorial social boundaries, sensu Carneiro (1970). Such circumscription is best evidenced by the development of local pottery styles, as I could identify. This economic and demographic process is in agreement with the “wave of advance” model for linguistic change: a population, bringing a new subsistence technology, grows to the point of displacing the previous inhabitants of a region. On the other hand, the yet few known cases of local adoption of agriculture and pottery by pre-existing inhabitants of Southern Brazil can be explained by evoking social and ideological factors possibly linked to the spread of a ritual complex typical of Jê societies, manifest in the construction of ceremonial centers with earthworks and burial mounds. This is in agreement with the “recruitment” model, according to which a language perceived as more prestigious spreads through language shift together with certain social and ideological features of its speakers. To explain the separation between the Southern and Northern/Central branches of the Jê family, similar archaeological studies and syntheses must be conducted in Central Brazil.