Glaciers can be considered slow-moving rivers of ice. They cover about 10% of the earth’s terrestrial surface and are concentrated in polar (e.g., Antarctica and Greenland) and alpine (e.g., Himalayas) regions (Fig. 6.1; Matthews, 1999; Boone, 2017). As glaciers flow they scour the landscape, altering the topography and drainage patterns. When they melt they leave behind typical features such as U-shaped valleys and various types of moraines. In, on, and under glacial ice there are many microorganisms and sometimes nonvascular and vascular plants, so recently deglaciated surfaces are far from sterile (Wynn-Williams, 1993). In fact, early successional heterotrophic microbial communities partially utilize carbon that predates the glacier (Bardgett et al., 2007). Nevertheless, after centuries of burial beneath ice and the violent churning that occurs during melting, deglaciated surfaces have little biological legacy, so they undergo primary succession. Although glaciers also affect many riparian habitats far downstream from a melting glacier (e.g., through scouring and deposition of sediments), we focus on terrain that was formerly under the ice. Natural forces largely drive glacial retreats but recent anthropogenic global warming has accelerated this process. The most thorough, global study of succession on deglaciated terrain was by Matthews (1992); physiological adaptations to the harsh environment are described by Körner (2003).