This chapter has shown how pairs of complex SAR images can be combined to generate several useful remote sensing products. The focus has been primarily on digital elevation maps, but it has also introduced ways to measure temporal changes in the profile or reflectivity of a scene on both short and long time scales using along-track interferometry, coherent change detection, and temporal motion mapping. All of these techniques rely on measurements of interferometric phase differences between images, differing in whether and how much those images are separated along spatial and temporal baselines. Because they all rely on IPD as the fundamental measured quantity, they share many common signal processing steps: subpixel image coregistration; two-dimensional phase unwrapping or its equivalent; filtering and multilook averaging for maximizing coherence; and orthorectification and geocoding to provide useful final data products. These mission concepts and processing techniques continue to be active research areas: InSAR is expanding into true 3-D imaging using Fourier, tomographic, and other methods, while ATI is expanding into combined GMTI and SAR. More advanced SAR sensors and the advent of formation and constellation sensor systems continue to expand the menu of measurement configurations. These developments mark progress toward a capability for timely, high-quality earth resources data acquisition as well as military and security surveillance, both on a global scale.