Over the past 15 years, software for processing interferometric synthetic aperture radar (InSAR) data into maps of surface deformation has been developed and refined. The InSAR technique is commonly used to investigate deformation associated with earthquakes, volcanoes, withdrawal of crustal fluids, and coherent ice motions [Massonnet and Feigl, 1998]. The software, called Generic Mapping Tools Synthetic Aperture Radar (GMTSAR), is an open-source (GNU General Public License) InSAR processing system designed for users familiar with Generic Mapping Tools (GMT) [Wessel and Smith, 1998]. The GMTSAR code is written in the C programing language and will run on any UNIX® computer. It requires installation of GMT and Network Common Data Format (NetCDF) and supports several fast Fourier transform libraries.