The Tax Crime Investigation Maturity Model aims to help jurisdictions understand where they stand in the implementation of the OECD’s Fighting Tax Crime: The Ten Global Principles, based on a set of empirically observed indicators. By setting out indicators for each increasing level of maturity, the model also charts out an evolutionary path for future progress towards the most cutting-edge practices in tax crime investigation across four levels of maturity: Emerging, Progressing, Established and Aspirational. It therefore also serves as an important tool for measuring the impact of tax crime capacity building interventions, including those promoted by the Addis Tax Initiative and G7 Bari Declaration. The model also has relevance for jurisdictions at all stages of development. The focal point of this Maturity Model self-assessment exercise is the tax crime investigation agency in a jurisdiction. However, given the strong linkages between tax and other financial crimes, the self-assessment will provide the most useful diagnosis when completed jointly with other relevant stakeholders from across a range of financial crime enforcement authorities, the prosecution agency and the policymakers. Thus, the whole of government approach is an integral part of the model.