thumb|400px|Fast ice (left, along shoreline) versus drift ice (right) in a hypothetical [[sea ice dynamics scenario (The bear provides an approximate scale.)]]
Fast ice (also called land-fast ice, landfast ice, and shore-fast ice) is sea ice or lake ice that is "fastened" to the coastline, to the sea floor along shoals, or to grounded icebergs. Fast ice may either grow in place from the sea water or by freezing pieces of drifting ice to the shore or other anchor sites. Unlike drift (or pack) ice, fast ice does not move with currents and winds.
The width (and the presence) of this ice zone is usually seasonal and depends on ice thickness, topography of the sea floor and islands. Further away from the coastline, the ice may become anchored to the sea bottom—it is then referred to as bottomfast ice.