Olduvai Gorge is a site in Tanzania that holds the earliest evidence of the existence of human ancestors. Paleoanthropologists have found hundreds of fossilized bones and stone tools in the area dating back millions of years, leading them to conclude that humans evolved in Africa.

Olduvai Gorge, Olduvai also spelled Olduwai, paleoanthropological site in the eastern Serengeti Plain, within the boundaries of the Ngorongoro Conservation Area in northern Tanzania. It is a steep-sided ravine consisting of two branches that have a combined length of about 30 miles (48 km) and are 295 feet (90 metres) deep. Deposits exposed in the sides of the gorge cover a time span from about 2.1 million to 15,000 years ago. The deposits have yielded the fossil remains of more than 60 hominins (members of the human lineage), providing the most continuous known record of human evolution during the past 2 million years, as well as the longest known archaeological record of the development of stone-tool industries. Olduvai Gorge was designated part of a UNESCO World Heritage site in 1979.