Abstract: This talk will address the kinds of work that gets done with categories in workplace interactions. Categories matter because people make sense of their professional relationships at work by using membership categories. Membership categories are the social classifications that may be used to describe a person and engage in inferences about them (Eglin & Hester, 1997; Stockoe, 2012; Fitzgerald & Housley, 2015). Crucially, when we use membership categories we also draw on and use a stock of knowledge and associated reasoning procedures about the kinds of activities, attributes, rights, responsibilities and expectations that are linked to those categories of person. In this talk, I will also aim to show how categories can be used to bring into being new relationships and new ways of organizing in workplace settings. We will delve into the murky world of organizational politics and managerial practice in one organization and explore the way that categories in talk enabled a change agent to manoeuvre himself and a team of managers through the politics of a strategic change project. After looking at the kinds of work accomplished by categories in this one case, I will conclude by drawing out wider implications for the study of categories – and their consequences – for professional practice in a range of institutional settings.