Three characteristics are essential to good measurement: reliability, objectivity, and validity. Reliability and objectivity were the focus of this chapter. A measurement has reliability when it is consistently the same for each person over a short period of time. Two types of reliability are applicable to norm-referenced tests: stability and internal consistency. Objectivity, the second vital characteristic of a sound measurement, is the degree to which different judges agree in their scoring of each individual in a group. A fair test is one in which qualified judges rate individuals similarly and/or offer the same conditions of testing to all individuals equally. Reliability of criterion-referenced test scores was also discussed. The definition of reliability and techniques for estimating reliability differ from those for norm-referenced test scores.