The diversity in classification schemes across countries has restricted the possibility of comparing waste inventories and led to difficulties in interpreting waste management practices, both nationally and internationally. To help improve this situation, the OECD Nuclear Energy Agency (NEA) developed a methodology that ensures consistency of national radioactive waste and spent fuel inventory data by presenting them in a common scheme in direct connection with accepted management strategy and disposal routes. This report provides the final version of the methodology and presenting scheme for spent nuclear fuel and the radioactive waste of all existing types. Additionally, there are recommendations in the report on how to enhance the comparability of national inventory data using the NEA methodology. The NEA support for joint efforts of the International Atomic Energy Agency and the European Commission on harmonisation of the reporting process by member countries to the Joint Convention and European Council Directive 2011/70 EURATOM is also presented in the report.