The amalgamation of the City of Montreal in 2002 required hard work to harmonize tax practices and decentralize local functions to newly amalgamated cities and historic neighbourhoods suddenly transformed into boroughs. The 2006 de-amalgamation added another level of complexity in the governance structure of the city, leading to the creation of the agglomeration. Using data from budgets and financial statements produced over the last twenty years, this article analyzes the evolution of fiscal centralization and decentralization processes that occurred through structures like the agglomeration and the boroughs of the City of Montreal. The analysis shows that the harmonization of tax rates within the new amalgamated city took place on a short period. The divergence in tax rates that remains in 2021 is mainly due to differences in the boroughs’ tax rates. The use of these taxes has contributed to increasing the boroughs’ financial autonomy. But their budgetary weight within the city steadily decreased over this period, showing a trend towards centralization. At the agglomeration level, financial indicators have been relatively stable since 2006. Our analysis shows that changes in governance structures have however enabled the City of Montreal to improve its relative position among the municipalities of the island of Montreal since the 2002 amalgamation.