Stable isotopes provide an independent assessment of paleoenvironments in the Omo-Turkana Basin. Stable isotopes track the flow of oxygen and carbon through ecosystems and accordingly are not directly related to changes in mammalian faunal composition or sedimentology. Therefore, isotope studies give insight into the paleoenvironmental conditions in which human evolutionary trends have been recorded. The development of stable isotopes as indicators of continental environmental conditions has proceeded in parallel with questions about the conditions of human environment. What was the vegetation? How hot was it? How dry? What were the diets of animals living among early humans? And most persistently, how important were "savannas" to early hominids? In this review, we take the opportunity to provide extensive background on the use of isotopes in anthropological sites. The application of stable isotope ecology to anthropological sites in the Turkana Basin has a long history, but in many ways the Omo-Turkana Basin has been a proving ground for the development of new proxy methods for understanding tropical terrestrial environments in the Neogene and Quaternary. For that reason, we also describe some of the fundamental aspects of isotope ecology that developed outside the field of paleoanthropology.