Voluntary mergers of local jurisdictions in Europe gained in importance in the last two decades. Existing research pays only minor attention to the local structural determinants for the explanation of municipal mergers. The paper assesses determinants in two distinct phases of a merger process, launch and implementation. The quantitative study of 245 municipalities in the Swiss canton of Fribourg shows that structural factors, such as economic wealth and population size explain the launch of a merger process but not its implementation. Differences between launch and implementation process could be explained by the varying importance of different actors in the two phases of a merger process. The results are of interest for the scholarly debate on municipal mergers and for political actors promoting local territorial reforms in their regions or countries.