This handbook was prepared with the objective of improving the understanding of the basis for the use of Standard Reference Materials (SRMs). While written from the viewpoint of a chemist, the basic concepts described are believed to be applicable to most areas of metrology. The handbook is arranged by section in a logical progression, starting with the basic concepts of precision & accuracy, followed by discussions of the calibration & quality assurance of the measurement process, the use of SRMs to evaluate various kinds of measurements, & the reporting of data with evaluated limits of uncertainty. Charts & tables.