This book introduces and defines radar interferometry with emphasis on imaging radar interferometers, illustrating the application of interferometric radar techniques to the solution of current geophysical problems. It describes the notation and coordinate systems used within the field, the importance of phase measurements, and provides a brief discussion of the parallel argument for point target scatterers. The book goes on to to introduce the concept of correlation of radar signals from different antennas, fundamental to the performance of any interferometer. Data processing issues related to the interferometric radar are also investigated. 3D radar, velocity image mapping, temporal variation, and the role interferometry plays in planetary radar studies are also covered in detail.