The article presents a summary of the present state of knowledge of perennial periglacial mounds, including descriptions of the external appearance and internal composition of pingos and palsas and a discussion of the genetic mechanisms. Pingos appear to be the result of the freezing of a mass of water trapped beneath permafrost under cryostatic or hydraulic pressure. Palsas are formed by the migration of groundwater to a freezing plane (cryosuction). The existence of mineral palsas is recognized; in this case the peat cover may be extremely thin or even totally non‐existent.