Municipal amalgamation reforms have been advocated as ways to improve efficiency, reduce costs, and enhance capacity in local government service provision. Research on the consequences of amalgamations has reached maturity in terms of theories, research designs and methods, justifying a systematic survey of results. This article provides a synthesis of the empirical literature published over the last 20 years, organizing the effects of amalgamations into three categories: economic efficiency and cost savings, managerial implications, and democratic outcomes. Despite the significant variation across countries and reforms, some regularities emerge: cost savings being primarily limited to general administration expenditures (wages, office supplies, and so on), few changes in the quality of local services, and the diminished quality of local democracy. Several studies point to amalgamation reforms experiencing a trade-off between efficiency and democracy.