Heat-flow values have been obtained at six new sites in Nova Scotia and New Brunswick. These values and six previously reported for Maritime Canada range from 45 to 79 mW m−2 (1.07 to 1.89 μcal cm−2 s−1) after correction for Pleistocene glaciation. The mean 62 ± 3 mW m−2 (1.48 ± 0.06 μcal cm−2 s−1) after a glacial correction and 54 ± 3 mW m−2 (1.29 ± 0.06 μcal cm−2 s−1) without the correction are in general agreement with the average for Paleozoic orogenic belts. High heat flows in New Brunswick are probably associated with acidic or felsic volcanics with high radioactive heat production. Low heat-flow values are associated with the deep Carboniferous sedimentary basin of Prince Edward Island and northwestern Nova Scotia. Probably the region was uplifted and the surface crystalline rocks with high radioactive heat production were eroded prior to Carboniferous time. During subsequent slow subsidence, low heat production sediments were deposited in the resulting basin. High heat flows in Nova Scotia are associated with the Devonian granites and the older Meguma sediments and metasediments, which have high radioactive heat production. The heat-flow data from Nova Scotia, together with estimates of the radioactive heat production of basement rocks, are consistent with the heat-flow–heat-production relations for the eastern United States, the Canadian Shield, and for other stable areas. The temperature at the base of the crust at 35 km depth is estimated to average about 750 °C.