The paleoenvironmental conditions that prevailed in the northwest North Atlantic regions and adjacent mainland Canada during the last interglacial are documented through lithostratigraphical and paleontological data in terrestrial sections and marine cores, with special reference to the deep-sea records that allow global correlations based on their isotopic stratigraphy. The onshore paleovegetational data and the offshore planktonic faunal and algal records demonstrate much warmer than present terrestrial and marine environments during the climate optimum of the last interglacial sensu stricto (Isotopic Substage 5e). Optimal conditions persisted in surface water of the Labrador Sea during the early glacial inception (Isotopic Substage 5e/5d transition) when extensive ice masses developed over Arctic Canada. A deterioration of sea-surface temperature in Labrador Sea followed the maximum 18O peak of Isotopic Substage 5d. During the later part of Stage 5, climatic conditions similar to the present prevailed over southeastern Canada and a recurrent warming is recorded in south central Labrador Sea; fluctuating ice volumes in the Canadian Arctic led to episodic dilution of surface water masses in Baffin Bay and the eastern Labrador Sea, and subarctic conditions apparently prevailed in nearshore environments of Baffin Island despite an ice marginal context.