The Hazard Modeller’s Toolkit (or HMTK) is a Python 2.7 library of functions written by scientists at the GEM Model Facility, which is intended to provide scientists and engineers with the tools to help create the seismogenic input models that go into the OpenQuake hazard engine. The process of developing building the hazard model is a complex and often challenging one, and whilst many aspect of the practice are relatively common, the choice of certain methods or tools for undertaking each step can be a matter of judgement. The intention of this software is to provide scientists and engineers with the means to apply many of the most commonly used algorithms for preparing seismogenic source models using seismicity and geological data. In forthcoming versions will hope to make available more tools for the current processes indicated here, and to integrate new functionalities for i) merging and homogenisation of earthquake catalogues, ii) calculation of activity rates from geological and geodetic data, iii) testing and interpretation of Ground Motion Prediction Equations, and iv) integration of seismological and geological data and treatment of uncertainty in the construction of seismogenic source zones.