Abstract: Over 40 years of diffusion worldwide, Environmental Impact Assessment (EIA) has acquired an authoritative governance script that says that part of the decision-making process about the licensing or the funding of territorial development projects can be delegated to the instrument. Inscribed in applicable planning and development law, regulations, and general technical reference documents, EIA affords its use for legitimizing and challenging decisions where a balance between competing environmental and developmental interests is to be struck. Initially associated with information provision for ecologically rational planning, EIAs became enshrined as a means, and ultimately a condition, for the substantiation of sustainable development and participatory governance, whatever these may mean. This chapter offers an original account of EIA as a technology that scripts collective action through black-boxing the politics of governance. After tracing the global trajectory of the instrument, the chapter looks at EIA struggles in the case of pulp mills on the River Uruguay. As actors seeking to halt projects because of their potential harmful impact follow the choreography of EIA, the authoritative governance script is reinforced rather than undermined. There is a tragic aspect to this, in that those wishing to block a project are actually making it stronger. This points to a subtle de-politicization resulting from the evolution of instruments in use, and a need for their re-politicization.