For more than 30 years, stable isotopes have been widely used to reconstruct the diet of Quaternary mammals and the environment where these animals lived. Carbon, nitrogen, and oxygen stable isotopes in the organic (collagen) and mineral (bioapatite) fraction of the skeletal tissues provide us with a proxy of what an animal ate and drank during some time in its lifetime, in which environment it inhabited and foraged, how it interacted with hominins and animals in its ecosystem, how keystone species could have shaped their environment, and how it could potentially have modified its ecological niche. This quantitative method also serves as a powerful tool to trace ecological, environmental and climatic differences across space and time, as well as their implications for human and mammalian evolution. New methodologies and isotopic markers improve the resolution and the time depth of this approach, opening new opportunities for past ecosystem reconstruction. In this session, we bring together researchers using stable isotopes to study the ecology of Quaternary mammals and extant species.