Different discourses that co-exist within the world of patient and public involvement in health and social care mirror a tangle of historical, social, political and theoretical roots. These range from the radical activism, born of civil rights movements, to a more passive model in which patients are the recipients of information. This paper explores the concept of 'representation' and the ways the concept is used by people serving as 'patient' or 'lay' representatives in a range of roles within research projects, funding bodies and academic institutions. We address the issue of why the representativeness of those involved is contestable. Drawing on qualitative research and engaged practice as well as on literature from social and political sciences we question how people conceptualise their own and their fellows' acts of representation. In doing this we identify nine different conceptualisations of what it is to represent and use these to explore how judgements are made about what can count as legitimate forms of representation.