Like more standard histories, archaeological histories begin at the beginning. As Chapter 2 notes, the archaeology of the Great Plains first found national attention in the early 20th century as sites like Folsom and Blackwater Draw produced incontestable evidence that humans lived side by side with extinct Pleistocene mammals. After nearly a century with this early occupation in the archaeological spotlight, it ought to be relatively straightforward to document the time and pattern of the first arrival of humans on the grasslands. Sadly, though, it is not, and identifying the beginning of human occupation of the Great Plains is as controversial as identifying the beginning of human occupation anywhere else in North America. This chapter reviews the evidence for the first peopling of the Great Plains in the context of the peopling of the New World as a whole and then turns to the environmental setting in which the first humans appeared in the region and the earliest definite evidence of human occupation on the Plains.