Radar interferometry measures changes in the Earth's surface by comparing phase differences between two radar images taken at different times. This technique provides high spatial resolution (about 100 pixels per km²), high precision (about 1 cm), and a useful observation frequency (one pass per month). It can detect crustal movements, atmospheric perturbations, soil dielectric changes, and topographic features. However, it is also sensitive to technical factors like radar trajectory variations and frequency standard changes. The paper describes how these factors contribute to interferograms and outlines techniques for processing and interpreting them. It discusses the use of four satellites (ERS-1, ERS-2, JERS-1, and RADARSAT) for interferometric applications. The paper also reviews geophysical applications, including earthquakes, volcanoes, glaciers, and landslides, and highlights the importance of understanding measurement uncertainties and artifacts. It concludes with perspectives on the future of radar interferometry, emphasizing the need for physical understanding and geophysical intuition to interpret interferograms effectively. The paper also discusses the limitations of interferometry, including the effects of topography, displacement, and atmospheric conditions, as well as the challenges of processing interferograms from different satellites and the importance of accurate orbital data. The paper provides a detailed overview of the technical and mathematical aspects of interferometry, including the principles of radar phase and interferometry, the construction and improvement of interferograms, and the interpretation of interferograms as geophysical measurements.Radar interferometry measures changes in the Earth's surface by comparing phase differences between two radar images taken at different times. This technique provides high spatial resolution (about 100 pixels per km²), high precision (about 1 cm), and a useful observation frequency (one pass per month). It can detect crustal movements, atmospheric perturbations, soil dielectric changes, and topographic features. However, it is also sensitive to technical factors like radar trajectory variations and frequency standard changes. The paper describes how these factors contribute to interferograms and outlines techniques for processing and interpreting them. It discusses the use of four satellites (ERS-1, ERS-2, JERS-1, and RADARSAT) for interferometric applications. The paper also reviews geophysical applications, including earthquakes, volcanoes, glaciers, and landslides, and highlights the importance of understanding measurement uncertainties and artifacts. It concludes with perspectives on the future of radar interferometry, emphasizing the need for physical understanding and geophysical intuition to interpret interferograms effectively. The paper also discusses the limitations of interferometry, including the effects of topography, displacement, and atmospheric conditions, as well as the challenges of processing interferograms from different satellites and the importance of accurate orbital data. The paper provides a detailed overview of the technical and mathematical aspects of interferometry, including the principles of radar phase and interferometry, the construction and improvement of interferograms, and the interpretation of interferograms as geophysical measurements.