Permafrost (permanently frozen ground) is largely present in mountain areas. Even though it is invisible, it is substantially more extended than glaciers (about 3 times more in the European Alps). Initially, permafrost was studied in the Arctic (Siberia, Northern Canada, Alaska) and mountain permafrost has been investigated since the 1970s only. Since the early 2000s, and notably since the hot wave that struck the European Alps in 2003, and was concomitant to a high frequency of rockfalls, scientists have raised interests for rockwall permafrost. For about two decades, investigations on rockwall permafrost have focused on assessing and mapping its distribution in various mountain ranges, assessing its recent and future evolution, as well as determining its role in rockwall destabilization. It is not yet possible to predict when and where permafrost dynamics will trigger rockfalls, but some evidences of the link between rockwall permafrost distribution and shortterm evolution have already been established. In parallel, the impact of increasing rockfall frequency on mountain practices and guiding activities have been demonstatrated, notably in the Mont Blanc massif which has become an outdoor and pilot laboratory for alpine permafrost researches. This presentation will introduce some basic concepts and knowledge about mountain permafrost, how it is distributed, how it evolves, how it may threaten mountain practices and the recent developments to assess the risks associated to its evolution.