A discussion about subsistence strategies and ethnic identities inspired the first study of diets with carbon and nitrogen stable isotopes in Tierra del Fuego. From this onwards, stable isotope analyses on human remains deepened the knowledge about the spatial variation of native diets. Furthermore, they proposed regional continuities where written sources projected discrete cultural boundaries between prehistoric groups of Beagle Channel and Península Mitre. The isotopic perspective also contributed to the reconstruction of ancient food webs previous to the industrial exploitation of pinnipeds, fisheries, and the introduction of livestock in southern South America. In this chapter, we synthesize 30 years of stable isotope analyses on these topics, focusing on the construction of local isotopic ecology, and the scopes and limitations of human paleodietary reconstructions in the southern coast of Tierra del Fuego. From these works, we highlight the role of human populations as consumers connecting the terrestrial and marine food webs, which gave us a better understanding of the flexibility of native groups facing major challenges such as industrial exploitation of fauna and contact processes during the Late Holocene.