Over 3 500 measurements of surface heat-flux have been catalogued and analyzed to study the large-scale variations of terrestrial heat-flow. It was found that heat-flow values are correlated with major geologic provinces: higher averages and scattered values in active tectonic regions, and lower averages and more uniform values in stable areas. Analyzing the data in the light of new global tectonics shows that the variations of heat-flow are consistent with the hypotheses of sea-floor spreading and plate tectonics. The observed heat-flow across the mid-oceanic ridges can be accounted for by a simple model of a spreading sea floor. ?? 1970.