The Geological Subsurface Toolbox (GeoST) package is designed to be an easy-to-use Python interface for working with subsurface data of The Netherlands, allowing you to integrate these data in your workflows for data analyses, modelling and visualisation. GeoST readily provides commonly used methods for e.g. spatial/conditional selections, conversions and data fusion, but at the same time remains fully flexible for advanced users to develop their own functions around GeoST data objects.