Reference materials play an important role in analytical chemistry, where they are used by analysts for a variety of purposes, including: checking and calibrating instruments; validating methods and estimating the uncertainty of analytical measurements; checking laboratory and analyst performance; and internal quality control. This book provides guidance and information for the users of certified reference materials (CRMs), explaining how they can best be used to achieve valid analytical measurements and improve quality in the analytical laboratory. General information on CRMs and how they are produced sets the scene for readers. The statistics relating to CRM use are then explained in an easy-to-understand manner, and this is followed by sections covering the main uses of CRMs. Detailed worked examples are used throughout.