The aim of this article is to analyse the process of expansion of the Belo Horizonte Metropolitan Area, created in 1973 with 14 municipalities, which today comprises 34 municipalities, making it the second largest MA in Brazil. After the redemocratization, more specifically after the promulgation of the State Constitutions in the late 1980s, several new metropolitan areas were created in the country, and all nine MAs instituted in the early 1970s increased their number of member municipalities, in a context of low prioritization of the MAs by the federal government. The article highlights the factors of a legal, institutional, symbolic and political/electoral nature that explain the expansion of the BHMA, also very present in other regions. It underscores the impact of the model of metropolitan management adopted after the 1989 State Constitution on the capacity to produce cooperative action in the metropolitan sphere. It also analyses the manner in which the dilemma of collective action for the management of the MAs in the state of Minas Gerais was sought to be overcome, by means of adopting a new institutional model, in the mid-2000s.