Magnetic Resonance Companion (MestRe-C) is a software package that offers state-of-the-art facilities for data processing, visualization, and analysis of high-resolution nuclear magnetic resonance (NMR) data, combined with a robust, user-friendly graphical interface that fully exploits the power and flexibility of the Windows platform. The program provides a variety of conversion facilities for most NMR spectrometer formats and includes all the conventional processing, displaying, and plotting capabilities of an NMR program, as well as more advanced processing techniques. A brief review of the basic concepts of NMR data processing is included also. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 80-96, 2003.