Mansour, J. A.Giordani, JulianMoresi, LouisBeucher, RomainKaluza, OwenVelic, MirkoFarrington, R.Quenette, SteveBeall, Adam2021-02-182021-02-182475-9066http://hdl.handle.net/1885/223244The modelling of long time-scale solid-Earth processes presents challenges on many fronts. Typically a large range of length scales must be resolved, and computational requirements can easily go beyond a desktop machine’s capability, even in 2-dimensions. Rheological behaviours are diverse and modellers often wish to investigate a spectrum of dynamics. With this also comes the requirement of robust solution strategies capable of capturing a system of large dynamic range. Time dependent aspects of a model also require careful consideration such that numerical artefacts do not subsume the required signal. Underworld2 is a Python API which seeks to meet these challenges, while also providing a friendly and intuitive interface to model development.Underworld development was financially supported by AuScope (https://www.auscope.org.au) and the Australian Government via the National Collaborative Research Infrastructure Strategy (NCRIS). Additional funding for specific improvements and additional functionality has come from the Australian Research Council (http://www.arc.gov.au). The Python tool-kit was funded by the NeCTAR eResearch Tools program.application/pdfen-AUAuthors of papers retain copyrighthttps://creativecommons.org/licenses/by/4.0/202010.21105/joss.017972021-08-01Creative Commons Attribution 4.0 International License (CC-BY).