has prepared this introductory document to promote the sound evaluation of measurement uncertainty through the use of the GUM and to provide a prelude to the GUM Supplements and other documents JCGM is producing [3, 4, 5, 6, 7, 8]. As in the GUM, this document is primarily concerned with the expression of uncertainty in the measurement of a well-defined physical quantity — the measurand — that can be characterized by an essentially unique value. The purpose of the GUM Supplements and the other documents is to help with the interpretation of the GUM and enhance its application. The GUM Supplements and the other documents are together intended to have a scope that is considerably broader than that of the GUM. This document introduces (a) measurement uncertainty, (b) the GUM, and (c) the GUM Supplements and other documents that support the GUM. This introductory document is directed at (a) calibration, testing and inspection laboratories in industry, and laboratories such as those concerned with health and the environment, (b) accreditation bodies, and (c) scientific disciplines in general. It is hoped that it will also be useful to designers, because a product specification that takes better account of inspection requirements (and the associated measurement) can result in less stringent manufacturing requirements. It is also directed at academia, with the hope that more university departments will include modules on uncertainty evaluation in their courses. As a result, a new generation of students would be better armed to understand and provide uncertainty statements associated with measured values, and hence gain an improved appreciation of measurement. This introductory document, the GUM, the GUM Supplements and the other documents should be used in conjunction with the “International Vocabulary of Metrology—Basic and General Concepts and Associated Terms” (VIM).