The tropical rainforest environment is nutritionally poor and tricky to navigate as compared to open habitats. This poses challenges for human subsistence. There has been little evidence to suggest that human populations relied on rainforest resources before the start of the Holocene, 10,000 years ago. Roberts et al. analyzed earlier fossil human and animal tooth enamel from Sri Lanka. The diet of these humans suggests rainforest rather than open-habitat foraging. Thus, humans were effectively exploiting rainforests in Sri Lanka since at least 20,000 years ago throughout periods of considerable climatic and environmental flux.Science, this issue p. 1246 Human occupation of tropical rainforest habitats is thought to be a mainly Holocene phenomenon. Although archaeological and paleoenvironmental data have hinted at pre-Holocene rainforest foraging, earlier human reliance on rainforest resources has not been shown directly. We applied stable carbon and oxygen isotope analysis to human and faunal tooth enamel from four late Pleistocene–to–Holocene archaeological sites in Sri Lanka. The results show that human foragers relied primarily on rainforest resources from at least 20,000 years ago, with a distinct preference for semi-open rainforest and rain forest edges. Homo sapiens’ relationship with the tropical rainforests of South Asia is therefore long-standing, a conclusion that indicates the time-depth of anthropogenic reliance and influence on these habitats.