The energy balance processes at a surface are reviewed in relation to the development of extreme temperature profiles that constitute the normal operating environment of a lichen. The specific nature of this operating environment, irrespective of altitude or latitude is emphasized and illustrated with a number of specific examples. These range from the ‘desert’ thermal environment following forest fire in low-arctic spruce-lichen woodland to boundary layer conditions at 2000 m, which is the environment of Rhizocarpon superficiale. The importance of winter temperatures and the ameliorating effects of snow cover and thallus colour are also related to the ecology and thermal environment of arctic and alpine lichens. Finally the thermal regime of corticolous and pendulous epiphytic lichens is discussed, again in terms of boundary layer and canopy microclimate. It is concluded that the thermal environment of a lichen largely interacts physiologically with the thermal tolerance limits of the dry thallus on one hand and the temperature optimum of net photosynthesis on the other.