In principle, a digital elevation model (DEM) describes elevations of various points in a given area in digital format. In this chapter, only raster GIS based DEMs are discussed. Data for generating a DEM can be acquired from different sources such as: ground surveys, digitization of topographic contour maps, conventional aerial photographic photogrammetry, digital photogrammetry utilizing remote sensing image data, UAV-borne digital camera, satellite SAR data etc. The fundamental principle involved is the concept of elevation being related to parallax as developed originally for stereo aerial photography. The DEMs have found numerous geologic applications.