Since 2002, ground and ground surface temperatures have been systematically measured in the mountains of Troms and Finnmark, northern Norway. These data were used to calibrate and validate a transient heat flow model and a spatial permafrost model, to address ground thermal development since the end of the Little Ice Age, as well as possible permafrost responses to anticipated future climate changes. Approximately 20 per cent of the land area is underlain by permafrost, and in Finnmark, permafrost in palsa mires seems to dominate. Both observations and modelling show that the present permafrost is mainly ‘warm’, with mean ground temperatures above -3 °C. Permafrost has warmed during the last century, and at one site our ground temperature observations show the degradation of permafrost over the intervening decade. The study identifies three major permafrost regions in northern Norway: (1) maritime mountain permafrost in western Troms; (2) continental permafrost above the treeline and in bogs in Finnmark; and (3) Low Arctic permafrost on the peninsula of Varangerhalvøya, forming a transition between the Scandinavian mountain-dominated permafrost in the south and the arctic permafrost towards the north and east. Copyright © 2013 John Wiley & Sons, Ltd.