This paper focuses on international treaty review conducted by expert monitoring bodies in the Council of Europe. Such monitoring bodies are composed of part-time experts and full-time international civil servants (secretariat) and are ubiquitous to the United Nations, Council of Europe and other international organizations’ (IOs) treaty implementation mechanisms. The study traces the development of monitoring of three conventions: European Social Charter, Framework Convention for the Protection of National Minorities, and Convention on Action against Trafficking in Human Beings. The analysis points out ways in which monitoring bodies adjust and shape the institutional and discursive environment they evolve in, always in close interaction with political actors. It looks at ways treaty bodies negotiate their role and working principles, by choosing, for instance, between judicial or mediator identity. The comparison uncovers the chosen identity and the corresponding interaction pattern between the monitoring body and political actors – political bodies in the Council of Europe and State Parties – as the key to their success or failure. From the overall identity the study zooms in on incremental decision-making (for example, changing operational procedures and standardizing formulations, or refraining from such changes) and micro-behaviors of experts and secretariats composing monitoring bodies. Following an organization-sociological approach within the institutionalist paradigm of IO scholarship, it shows how these decisions and tactics enhance or diminish their authority and, as a result, the quality of treaty review.