Radar interferometry, a geophysical technique that calculates the interference pattern between two images acquired by a spaceborne synthetic aperture radar at different times, has seen significant growth in the early 1990s. This technique provides high spatial sampling density, precision, and observation cadence, making it useful for monitoring crustal movements, atmospheric perturbations, soil dielectric changes, and topographic relief. The resulting interferograms are sensitive to various phenomena, including technical effects such as variations in the radar's trajectory or frequency standard. The authors describe the principles of radar interferometry, the techniques for calculating and manipulating interferograms from various radar instruments, and guidelines for interpreting interferograms as geophysical measurements. They also review applications of radar interferometry to study deformation related to earthquakes, volcanoes, and glaciers, as well as natural hazards and environmental changes. The review concludes with perspectives on the future of radar interferometry, emphasizing the importance of understanding the physical processes involved in interferogram calculation and interpretation.Radar interferometry, a geophysical technique that calculates the interference pattern between two images acquired by a spaceborne synthetic aperture radar at different times, has seen significant growth in the early 1990s. This technique provides high spatial sampling density, precision, and observation cadence, making it useful for monitoring crustal movements, atmospheric perturbations, soil dielectric changes, and topographic relief. The resulting interferograms are sensitive to various phenomena, including technical effects such as variations in the radar's trajectory or frequency standard. The authors describe the principles of radar interferometry, the techniques for calculating and manipulating interferograms from various radar instruments, and guidelines for interpreting interferograms as geophysical measurements. They also review applications of radar interferometry to study deformation related to earthquakes, volcanoes, and glaciers, as well as natural hazards and environmental changes. The review concludes with perspectives on the future of radar interferometry, emphasizing the importance of understanding the physical processes involved in interferogram calculation and interpretation.