This chapter presents the seasonally frozen ground and permafrost. Frozen ground is a practical issue in the seasonal snow and ice zone due to ground deformation during freezing and melting. Scientific research on permafrost started in the nineteenth century in Siberia and, soon after, in North America [1]. In the twenty-first century, Chinese scientists have been very active on this topic due to their large mountain permafrost areas, especially in the Tibetan Plateau. Early research was motivated by observations indicating that the temperature increases with depth in the non-frozen ground at temperate latitudes. Permafrost was an exception requiring explanation. Later, various construction and engineering projects in the permafrost region have required advanced knowledge of its properties and evolution.