The ONIOM method, developed in the group of Keiji Morokuma, is one of the most successful examples of quantum mechanics/molecular mechanics (QM/MM) treatments, and of multilayer methods in general. Its implementation in the Gaussian program package is in particular widely used. This implementation has access to the wide variety of QM methods available in Gaussian, but is limited to only three specific force fields. The current article presents the GARLEEK interface, which expands the availability of molecular mechanics methods to the wide variety of force fields available in MM packages. The focus is in the simple installation and use. Two examples of the performance of the interface with selected systems are provided. GARLEEK is MIT-licensed and freely available at https://github.com/insilichem/garleek. (c) 2018 Wiley Periodicals, Inc.