This research program is devoted to the development of an international “peace engineering” since the aftermath of First World War. It consists in a set of academic science, pragmatic knowledge and recommendations aimed to restore peace into societies torn by armed conflicts and political violence. Such practical knowledge inspires scientific and technical developments by actors located either at the heart or the edge of the academic field, especially in the legal, military, diplomatic and religious "sciences". This knowledge is action-oriented and aims to implement standard techniques of pacification, in various forms: legal or diplomatic negotiation techniques, truth and reconciliation commissions, local programs to build and disseminate a “culture of peace", techniques of prevention of conflicts, rules of engagement in peace operations, etc. Rather than questioning the content of this knowledge and its efficiency, this research focuses upon their producers. It intends to reconstruct their careers within the different international organizations in which these producers are appointed. Without neglecting former practices in that realm (formalization of international law, religious missions ...), we can observe the deployment of an engineering of peace as it is subject to an overall institutionalization, through interstate interactions, scientific exchanges, and the establishment of international bureaucracies. This brings to question the specific logics at work in the constitution of genuine international careers of “professionals of peace” and in the process of international diffusion of knowledge and technology related to the pacification of societies. This program thus proposes a sociological insight on international relations, and especially on international organizations and the professional agents that make them exist. It will endow with enough empirical material as to test empirically a compelling hypothesis: the growing autonomy and empowerment of an international sphere relatively to national social sectors. The hypothesis will be tested through an in-depth empirical investigation, following a threefold movement: first a quantitative “prosopographical” analysis of careers through large-scale biographies in the field of international peacemaking, then a historical study of the main places of their academic and professional training, and lastly an observation of some of these professionals’ practices and trajectories – and especially the process whereby some of their outputs (of different forms: bureaucratic or legal knowledge, games and large-scale simulations) are broadcasted internationally.