This note describes the updated OECD FDI Regulatory Restrictiveness Index (FDIRRI) methodological framework, approved by the OECD Investment Committee in 2022 and which has been used to compute the new FDIRRI series released in 2024. First established in 2003, and last revised in 2022, the FDIRRI measures discriminatory restrictions on foreign direct investment (FDI) across countries and over time. It is a useful indicator for benchmarking market access and other statutory barriers to FDI and for monitoring and showcasing FDI policy reform efforts. As a policy-based indicator, the FDIRRI can also be used to empirically assess and simulate the potential impacts of FDI regulatory reforms. This note provides details on the revised FDIRRI methodology and highlights the main changes implemented in relation to the previous methodology.