What determines the success of federal arrangements? Federal arrangements are often introduced in contexts that lack multi-party democracy and instead are characterized by centralisation and limited competition in the context of a dominant party system. This uneasy combination of regional autonomy on the one hand and centralisation on the other alters federal dynamics significantly, most visibly in different modes of access to political power, procedures of political representation and consultation, and rules underlying political decision-making. The Ethiopian federal system serves as an empirical illustration for how intra-party politics takes precedence over federal institutions. Most importantly, original interview data collected during fieldwork suggests that the prevalence of party structures and procedures rather than formal federal institutions results in a system that provides relative stability, however interferes with regional autonomy. The findings underline the broader relevance of extra-constitutional factors for comparative analyses of the workings and success of federal systems.