This paper describes the methodology used to build the WJP Rule of Law Index – a new quantitative assessment tool designed to offer a comprehensive picture of the extent to which countries adhere to the rule of law in practice. The WJP Rule of Law Index provides new data on nine dimensions of the rule of law − limited government powers, absence of corruption, order and security, fundamental rights, open government, regulatory enforcement, access to civil justice, effective criminal justice, and informal justice − and is compiled from original surveys of the general public and local legal experts. The paper also presents estimates for an initial group of 66 countries.