The non-observed economy comprises production activities that are illegal, underground, informal, or otherwise missed by the statistical system. Unless efforts are made to deal with such activities, economic indicators are under estimated. This can be a serious issue, particularly in transition and emerging economies. Given the miscellany of possible approaches, there is a need to identify and promote international best practice. This is the aim of the Handbook for Measurement of the Non-Observed Economy.

The Handbook has been prepared by a team of experts from the OECD, the International Labour Organisation, the International Monetary Fund, the Interstate Statistical Committee of the Commonwealth of Independent States, the Italian National Statistical Institute, Statistics Netherlands, the Russian Federation State Statistical Committee, and the University of Versailles. A working draft of the Handbook was the subject of a Non-Observed Economy Workshop organised jointly by the OECD, Eurostat and the Russian Federation State Statistical Committee in Sochi, October 2000.

Following the publication of several studies on estimates of the underground economy, the international organisations that co-signed the well known "SNA 93" drafted the following official declaration.