The ML-PACE package provides the pace pair style, an efficient implementation of the Atomic Cluster Expansion potential (ACE). ACE is a methodology for deriving a highly accurate classical potential fit to a large archive of quantum mechanical (DFT) data. This package was written by Yury Lysogorskiy and others at ICAMS, the Interdisciplinary Centre for Advanced Materials Simulation, Ruhr University Bochum, Germany (http://www.icams.de). This package requires a library that can be downloaded and built in lib/pace or somewhere else, which must be done before building LAMMPS with this package. Details of the download, build, and install process for this package using traditional make (not CMake) are given in the lib/pace/README file, and scripts are provided to help automate the process. Also see the LAMMPS manual for general information on building LAMMPS with external libraries using either traditional make or CMake. More information about the ML-PACE implementation of ACE is available here: https://github.com/ICAMS/lammps-user-pace