While many governments are now committed to release Open Government Data under non-proprietary standardized formats, less attention has been given to the actual consequences of these standards for knowledge workers. Unpacking the history of three open data standards (CSV, GTFS, IATI), this paper shows what is actually happening when these standards are enacted in the work practices of bureaucracies. It is built on participant-observer enquiry and interviews focussed on the back rooms of open data, and looking specifi cally at the invisible work necessary to construct open datasets. It shows that the adoption of open standards is increasingly becoming an indicator of the advancement of open data programmes. Enacting open standards involves much more than simple technical operations, it operates a quiet and localised transformation of bureaucracies, in which the decisions of data workers have substantive consequences for how the open government data and transparency agendas are performed.