This chapter focuses on the use of Synthetic Aperture Radar (SAR) imagery to detect and quantify surface displacements on active volcanoes. It provides some basic information on the principle and geometry of SAR imagery before detailing how surface displacement maps can be retrieved from the combination of two time-offset acquisitions, either by using phase difference, thus producing interferograms, or by characterizing amplitude shifts by pixel offset tracking. The temporal evolution of the surface displacements can be obtained from the time series analysis of a large number of SAR images. The topic of interpreting displacement fields in order to derive key information in terms of magma storage at depth and transport to the surface by modelling is then widely covered. In particular, the influence of the geometry, position and orientation of the magma source, as well as the acquisition geometry and wavelength of the radar, on the fringe pattern of the interferograms is illustrated on the basis of synthetic cases. The chapter concludes with an overview of the current state of near-real-time volcano monitoring using SAR imagery in observatories and the main challenges that remain.