This chapter clarifies (Tests, scales and testing) these terms and outlines the general logic of testing and give some general information about the principles of testing and test administration together with some practical guidance about how to locate tests. Each test also comes with instructions for scoring it using a standardised method, which in practice usually means turning the participant's responses into some type of numerical scores. A scale consists of group of items whose scores are combined. It should be obvious that all of the items which form a scale should measure the same trait or state. A scale is therefore a collection of items which all measure the same trait, state, ability or area of knowledge – some domain, in other words. The number of items in the domain can vary. The aim of any scale is to estimate a person's true score, the score which they would obtain if they answered all possible items in the domain.