As North America's largest, high-elevation lake, Yellowstone Lake, Wyoming, played an important role in the lifeways of Great Plains, Great Basin, and Rocky Mountains Native Americans during prehistory. Various hypotheses suggest that the lake was important during the spring for fishing, during the winter for hunting, and/or during warm months for generalized foraging. Because the lake's islands contain archaeological sites, some also have proposed that boats were utilized during prehistory at the lake. Using ethnohistoric, archaeological, and spatial data, we evaluate these suppositions about use of Yellowstone Lake. We suggest that annual use of the lake was initiated in early spring when the lake was frozen providing access to islands and continued through the summer. Lithic data and ethnohistoric research support the hypothesis that multiple ethnic groups used the lake in prehistory because it is a concentrated resource area.