The chapter addresses changes to the environmental monitoring institutions for the mining sector in the province of San Juan, Argentina during the period 1993 to 2020. From a qualitative perspective, the main factors that have motivated the institutional transformation of environmental monitoring of mining are analyzed: coercion by international agencies (1993–2002), socio-environmental conflicts (2003–2014), and mining accidents (2015–2019). These external factors prompted the creation of regulations and bureaucratic departments for the environmental oversight of mining that did not previously exist at the subnational level. However, I argue that the political decision by the authorities in San Juan to prioritize mining led to a reactive institutional change that limited the capacity for environmental oversight as well as the means to respond to public demands for transparency and participation. The analysis shows that the political dimension is key to understanding the reactive institutional change process and in particular the weakness of the environmental oversight institutions for mining in San Juan.