Given that all large scale assessments (LSAs) have to address the 13 elements of a robust assessment programme, why and how do these assessments differ from one another in practice? The answer to this question lies in the way that the purpose and guiding principles of an assessment guide supports decisions about who and what should be assessed. In this chapter, Dara Ramalingam outlines the key features of a selection of LSAs to illustrate the way in which their different purposes and assessment frameworks have led to key differences in decisions about test content, target population and sampling.