This chapter presents the geophysics of the seasonal snow. Snow crystals form in the atmosphere, fall due to gravity, and accumulate onto the Earth’s surface producing the seasonal snow cover. This white, soft layer is a specific winter environment, and it protects the ground from cold and light. Snow–atmosphere interaction and snow metamorphic processes bring major changes to snowpack. The lifetime of seasonal snow is, by definition, less than 1 year, and at the final melting, seasonal snow returns in liquid phase to the global water cycle. Surviving over the summer, seasonal snow becomes firn and forms a layer of perennial land ice treated in Chap. 6 (Portrait 4.1).