Abstract <p>A review of Quaternary sediments, paleogeography and modern, mostly permafrost-related landforming processes has been made for Yamal and Gydan Penisulas, western Siberia. Yamal and Gydan peninsulas are situated in the north of Western Siberia, being part of an epi-Hercynian platform. Their lowlands are very flat; Quaternary perennially frozen deposits form their continuous cover. The composition, stratigraphy and origin of the sediments is patchy. Different geological bodies often compose the same level of topography, which often leads to varying interpretations of the origin and age of the same geological bodies. The Pleistocene and Holocene history of the area has seen dramatic changes, with rising and falling sea level, warming and cooling, disputed formation of ice sheets, lake development and intense fluvial erosion. Modern landforming processes can reach considerable rates, threatening human activity, and are mainly caused by permafrost aggradation and degradation: the most intense are thermoabrasion (coastal erosion), fluvial thermoerosion, thermokarst, frost heave, solifluction and formation of retrogressive thaw slumps; their linear velocities can reach dozens of meters a year.</p>