Research about the development of ethnic identifications within contexts of employment has been neglected, not least by proponents of ‘new ethnicities’. Drawing on evidence from a two year study of Black Police Associations in the constabularies of England and Wales, this paper is concerned with the construction and sustaining of a particular notion of ethnicity, related to police employment. Black Police Association members have claimed a distinct experience of police employment related directly to their being ‘black’ and, therefore, an essentialism forming a boundary marking them off from white officers. ‘Police ethnicity’, however, is a strategic notion that is somewhat fragile and exclusive. The consequences of BPA definitions of being a black officer are explored. The paper ends with a consideration of the wider, intellectual consequences of researching ethnicity within employment.