This chapter considers what the authors mean by 'measurement' and whether it is ever possible to say that test scores 'measure' traits and states. Joel Michell provided a devastating critique of psychological measurement theory; his paper should be read by all test users. Michell approaches the problem from the viewpoint of the philosophy of science. The chapter explores how one might interpret one person's score on a particular test. When testing children, some tests still use 'age norms'. The fact that z-scores are often negative confuses some simple-minded practitioners–particularly in education. To avoid this problem, they developed something called the T-score; note that this is nothing to do with the t-test in statistics or T-scaling. The chapter argues that scores on psychological tests are probably better regarde.