Evidence for environmental conditions in the Saint Lawrence Valley between 8,000 and 3,000 B.P. comes from three sources: (1) pollen stratigraphy, (2) macro and microfossils found at archaeological sites, and (3) association of the latter with geological features that can be used to reconstruct conditions of occupation. The Archaic Period is included in the Hypsithermal interval when assumed mean annual temperatures exceeded those of the present. Evidence available from pollen data suggests that the early inhabitants of the Saint Lawrence Valley were not influenced by this phenomenon as there is no agricultural activity before 3,000 B.P. Some changes in the cultural systems may be related to climatic fluctuations but the nomadic way of life prevailed throughout the whole period. The Archaic Period is divided into four subperiods: the Early Archaic, which is contemporaneous with the Late Paleoindian Period, extends from 10,000 to 8,000 B.P.; the Middle Archaic (8,000 to 6,000 B.P.); the Late Archaic (6,000 to 4,000 B.P.); and the Terminal Archaic (4,000 to 3,000 B.P.) By 8,000 B.P., freshwater species were available in the valley as well as in numerous lakes of the Canadian Shield where the Atlantic salmon ( Salmo salar) had become landlocked. Large mammals like deer, moose, and caribou were available in the forest from the Great Lakes to Gaspé, as well as beaver, porcupine, and hare. The present configuration of the Saint Lawrence River system was probably attained between 8,000 to 6,000 B.P. in the Montréal area. After 7,000 B.P., only minor fluctuations of the water level are recorded. However, these variations had great impact on the archaeological record. Many known archaeological sites are associated with beach ridges at low level along the shores of the Champlain and Goldthwait Seas or the ancestral Saint Lawrence River. The Archaic Period was characterized by a permanent occupation of the lowlands bordering the Saint Lawrence and by a growth in total population. The relations between physical environments and cultural systems are thus crucial if we want to discuss the evolution of adaptive strategies in the Saint Lawrence Valley where minor fluctuations of water level drastically change the landscape.