This paper explores the identities of Mass Observation diarists and directive respondents from the early project to 2011. It attempts to briefly examine demographic characteristics of MO writers and compare both early and recent projects. Contemporary identities and the demographic profile of the wider population are compared. This paper is important because it explores the impact that the search for types of ‘representativeness’ has had upon the historiography and use of MO as a source by scholars from multiple disciplines. It argues that criticisms of MO as unrepresentative have placed limits upon the ways that MO writing has been used. The conflict between criticisms of MO as unrepresentative will be compared with the views of MO correspondents of their own identities. The identities they have negotiated through their own writing are highlighted, including what it has meant to be ‘ordinary’ or to represent certain groups. The findings of this paper have implications for the ways in which scholars might use MO sources in the future. Suggestions will be made for new areas of research within MO, including ways in which new methodological approaches might be developed.