As with many countries, the UK is attempting to allow wider participation in higher education for all social groups. UK universities are increasingly making decisions about undergraduate admissions with reference to contextual indicators which are intended to identify whether or not an applicant comes from a disadvantaged family, neighbourhood or school environment. However, the indicators used are often chosen because they are readily available, without much consideration of the possible alternatives. This chapter suggests which of the potential contextual indicators are worth pursuing and which are not of high enough quality or might lead to greater injustice. It is based on a large systematic review of prior international evidence, and individual-level student statistics for all students in England from 2006 onwards.