This Review of Open Source and Open Access Software Packages Available to Quantify Risk from Natural Hazards is an Understanding Risk (UR) publication created by the GFDRR Innovation Lab intended for a technical audience. It aims to highlight modelling tools’ strengths and also highlights some of the challenges that a user of a modelling tool might face. Through UR, GFDRR seeks to provide initial guidance to users on the appropriateness of the various modelling tools for specific purposes and offers an introduction to the connectivity that is possible between the models. Finally, the document highlights where collaborative efforts between modelling tool developers could substantially improve our current understanding of risk.