Abstract The rugged Canadian Cordillera has been and is being created by various dynamic processes that are dominated by past and present plate-tectonic motions and interactions. A summary of the tectonic models proposed for the Cordillera, together with the geologic record and geophysical data that support them, is given by Gabrielse and Yorath (DNAG volume: Geology of Canada Series: Cordilleran Orogen, Canada, in preparation). In this active area the heat flux is determined by various regimes and processes, and the reduced heat flow is a diagnostic indicator of the state of the lithosphere. In general, the heat flux is decreased by subducting plates, increased by uplift and erosion, and increased and decreased, respectively, by exothermic and endothermic reactions occurring within the crust. It is quite variable over small areas where crustal intrusions are advectively cooling. Relatively high heat flux occurs in regions that are undergoing crustal extension. The magnitude of these variations can be used to evaluate the rates at which these processes are occurring and/or to infer other details concerning the complex evolution of this region. Current plate interactions along the western margin of the Canadian Cordillera (Riddihough and Hyndman, in preparation) are indicated in Figure 1. South of the triple junction, the Juan de Fuca plate is subducting under southern Vancouver Island and the coastal mainland; the smaller Explorer plate broke away and has now ceased to subduct. North of the triple junction, there is right-lateral transform movement along the Queen Charlotte fault with a small amount of oblique