When the merged union UNITE HERE was recently torn apart by internal dissent, the labor movement's attention turned to some longstanding questions about how union mergers are negotiated, why some fail and others succeed, how members are affected by merger, and how the big, diverse unions created by mergers-the super-unionsmanage to stay intact. This article addresses these questions, arguing throughout that little is actually known about the union merger process and outcomes. In doing so, it also suggests that some union mergers, such as the one forming UNITE HERE, may not always make sense and that bigger unions created by mergers are not necessarily better unions.