In this paper the results of several pollen analyses and related invertebrate studies are utilized in an attempt to reconstruct the nature of the Great Plains environment prior to and during the advent of man. A large sample of Early Man sites is then examined and conclusions are drawn concerning man's use of this environment. Specific problems considered include: the types of sites, where the sites are located, the types of animals hunted, hunting techniques, butchering techniques, and tool manufacture. It is concluded that the environment consisted of a savanna grassland with abundant ponds and streams bordered on the north and west by pine and occasional spruce trees. The stream valleys sheltered galleries of junipers and oaks. On this grassland lived large herds of Pleistocene animals now extinct. Climatic indicators suggest that the summers were cooler than today, with winters warmer than at present. A Paleo-Indian cultural tradition adapted to the utilization of this environment, primarily through big game hunting, was practiced on the Great Plains during the time interval represented by the Llano, Folsom, and Parallel Flaked horizons. During this entire interval, the type of sites, site situations utilized, hunting techniques, butchering techniques, and most of the tool inventory remained constant.