An emerging tool of global governance, Social and Environmental Safeguards (SES) expertise is growing within the international development field. While they initially came as an answer to Non-Governmental-Organization (NGO) campaigns and media attention which had led to an increasing perception of serious deficiencies in development projects led by International Organizations (IOs), they soon became an integral part of IOs' knowledge practices. While most research looks at the results, and effects of expert knowledge, this research aims to look at the practice, at how safeguard expertise is actually made, assembled, and how different actors and material elements are brought together to discuss unintended effects. The orientation of this project on the 'how' means that safeguard expertise is not perceived as being an essential manifestation of good governance. It is rather conceived as a technopolitical answer in a complex powerplay between different actors. To explore how SES expert knowledge is assembled, this research will build on STS and IR literature on assemblage, looking at how heterogeneous human and non-human elements interact to form a coherent body of knowledge. It will however locate this assemblage in the larger field of international development, using a bourdieusian perspective to shed light on power relations and domination mechanisms, in order to decipher what these relations may tell of IOs' governmentality. Further research how IOs assemble this expertise could lead to better understand how IOs expert knowledge practices functions and ultimately, provide clues on how improve their practices.