||Portfolios are an increasingly common form of assessment, particularly in education (van der Schaaf and Stokking, 2008; Baume and Yorke, 2002; Mclean and Bullard, 2000) but also in professional courses like medicine and law (eg Driessen and van der Vleuten 2000; Driessen et al, 2005). Our experiences of using portfolio assessment in Higher Education are within educational development programmes designed to encourage doctoral students or lecturers to adopt a reflective approach to their professional practice (see, for example, Boud and Walker, 1998). In these programmes, the portfolio approach is intended to allow participants from a range of backgrounds and disciplines, with different levels of experience and expertise, to compile a document which is meaningful to them within their given context. However, there are several challenges associated with portfolio assessment and we would like to explore these more fully in this discussion paper (see, for example, Baume, 2001 or Elton and Johnston, 2002). We are, in part, concerned with some of the common debates surrounding the reliability and validity of assessment practices more broadly. However, we will argue that these general concerns are often exacerbated in the case of portfolios which are, by their nature, intensely personal documents intended to signal the learning and personal transformation experienced (or not) by our participants (see Baume and Yorke, 2002). The metacognitive skills that the portfolio is supposed to represent are difficult to pin down and assessors have to rely heavily on qualitative professional judgement when making assessment decisions (see, for example, Driessen et al, 2005). In terms of portfolios as a valid approach to assessment, issues of authenticity become central 'how does one judge whether the portfolio represents an authentic experience, or is simply an effort to play the assessment game?' Are there signifiers of authenticity? that we might look for to help us to distinguish which participants have really developed the reflective insights and capacities that we aim for in our courses? These are the questions that we hope to address with reference to our own practice as assessors of portfolios.