The USER-MSCG package adds a fix mscg command, which carries out multi-scale coarse-graining for the parameterization of coarse-grained (CG) interactions. It uses the Multi-Scale Coarse-Graining (MS-CG) library, available at https://github.com/uchicago-voth/MSCG-release. The MSCG library was developed by Jacob Wagner in Greg Voth's group at the University of Chicago. The library can be downloaded and built in lib/mscg or elsewhere on your system, which must be done before bulding LAMMPS with this package. Details of the download, build, and install process for MSCG are given in the lib/mscg/README file. Also see the LAMMPS manual for general information on building LAMMPS with external libraries. The settings in the Makefile.lammps file in lib/mscg must be correct for LAMMPS to build correctly with this package installed. There are example scripts for using this package in examples/mscg.