Kelly has shaped and contributed much to our understanding of hunter-gatherer societies. He has a deep interest in Western North American archaeology, especially in the Great Basin area. Current understanding of hunter-gatherer mobility and foraging patterns are also influenced strongly by his research, fieldwork, and ethnology. By examining the Pleistocene colonization of the Americas by examining artifacts and lithic technology, Kelly reconstructs past life-ways and compares them to current foraging societies, and examines human adaptation to climate change during different periods in the past.
