QMCube is a suite written in the Python programming language initially focused on multiscale QM/MM simulations of biological systems, but open enough to address other kinds of problems. It allows the user to interface and combine highly efficient QM and MM programs, providing a unified access to a wide range of computational methods. The suite also supplies additional modules with extra functionalities which facilitate common tasks such as performing the setup of the models, or processing the data generated in the simulations. It has been designed considering the lowest number of external dependencies (just an algebra library, included in the distribution), which makes it extremely portable. In addition, the different modules have been structured in such a way that it should be easy to expand the suite, and develop new computational methods. Please include this reference in published work using QMCube: Martí, S. 'QMCube (QM3): An all-purpose suite for multiscale QM/MM calculations' J. Comput. Chem. 2021, 42, 447-457 [10.1002/jcc.26465] https://onlinelibrary.wiley.com/doi/full/10.1002/jcc.26465