This paper examines the way international secretariats strategically resort to the use of expert knowledge in order to expand their remit and promote their own agendas in new issue areas. If the role of knowledge as a constitutive element of bureaucratic authority has well been captured, there is a lack of conceptualization on the way international bureaucracies strategically mobilize expert knowledge. Is knowledge used instrumentally to adjust policy outputs, more symbolically to assert international bureaucracies’ epistemic authority, strategically to justify their jurisdiction into new policy domains, build their capacity to act or boost certain claims, or as a means to depoliticize contentious policy issues? While some of these different uses of knowledge might overlap in practice, there is a need to at least analytically distinguish between different modes of knowledge mobilization. This paper addresses this gap in the existing literature on international bureaucracies. It does so by examining the sector of bioethics, a particularly hard case of international bureaucratic expansion. It shows that the use of a new type of expertise, aimed at guiding policy on the ‘right’ ethical path, rather than advising specific policy choices on grounds of scientific rationality, made the expansion of technocratic decision-making to bioethics possible and allowed international bureaucrats to take on a new role, that of shapers of moral standards in issues brought about by scientific innovation. If even in areas in which ethical questions are explicitly laid out international bureaucrats are able to assert their grip on policy, this makes a case for the their ability to act as policy-makers and for the efficiency of involving experts into the policy process. Because it can simultaneously boost their capacity to act, endow their policies with epistemic authority, depoliticize issues and act as a tool of policy dissemination, expert knowledge is an ideal tool in the hands of bureaucrats who wish to control new issue areas and promote certain agendas.