Measurement procedures can be placed on a continuum stretching from representational at one end to pragmatic at the other. Measurements in the physical sciences tend to have a heavier representational aspect, and those in the social and behavioural sciences more pragmatic. In many cases, measurement consists of a mixture of the two extremes. ‘What is measurement?’ introduces these two concepts of measurement and the properties of each perspective. Representational measurement defines a mapping from the real world to the numerical world, so that relationships between numbers represent relationships between the things being measured. Pragmatic measurement simultaneously defines an attribute and describes how to measure it.