The field of quality assurance is beset by an extensive and sometimes confusing terminology, the use of which has still not been universally agreed on or accepted by laboratories or interested professional bodies worldwide. This glossary contains some of the most commonly used expressions in these fields, including those which appear in UNODC publications on quality assurance, and is an attempt to help promote and harmonize national efforts by providing internationally acceptable terminology. It is intended to be an aid to analysts in the implementation of quality assurance programmes and good laboratory practices, and as a means of encouraging laboratories to collaborate and participate in quality assurance matters. As a result, the Glossary includes more than one definition of a word or phrase where these might improve understanding of what they mean. This publication is an update of the first edition of the Glossary of Quality Assurance Terms.