This guide explains methods for undertaking the measurement of mass, one of the most frequent operations in the analytical laboratory. It is a technique required when obtaining a known quantity of a sample for analysis; for preparation of analytical reagents; and for preparation of calibration standards. After an initial discussion of the units of mass and other terminology, the guide goes on to look at the types of balance and their features, followed by coverage of location, calibration, accuracy and use of the balance. Practical exercises are then provided. "Measurement of Mass" is one of the "Practical Laboratory Skills Training Guides", a series that aims to make achieving best practice easy. These manuals will enable both experienced and inexperienced staff to get the essential basics of any experiment right simply by following the clear and easy to use instructions provided. The guides are written by experienced scientists and include minimal theory, plenty of practical exercises in order to assess competence, and trouble-shooting information.