This chapter offers a personal reflection on the nature of impact, based on the author’s substantial experience of being involved in impact-focused research. The chapter begins with a definition of impact that relates to the UK Research Excellence Framework, before going on to consider a range of issues related to the concept. These include the difference between impact and dissemination, inhibitors of impact, and the problem of sourcing evidence for claims about the impact of a piece of research. These issues are discussed both in the abstract and with reference to a genuine case study of corpus research at Lancaster University, submitted to the 2014 REF.