In this article, we offer an explanation for varying patterns of territorial reforms aimed at accom modating claims for more substate autonomy in multinational states.We argue that the interaction between preferences of state wide and non statewide parties, their negotiation power and the negotiation mode accounts for specific patterns of territorial change. Analytically, we advance existing research in two ways: First, by analyzing territorial change in a two dimensional space (vertical and horizontal), we pay explicit attention to jurisdictional heterogeneity between substates. Second, by applying an actor centered institutionalist approach, we highlight the stra tegic potential of actors within the institutional setting. The comparative analysis of thirteen processes of territorial change in four multinational Western democracies Canada, Belgium, Spain, and the UK reveals, first, certain conditional effects of the independent variables on specific patterns of territorial change and, second, how the negotiation mode impacts on a party's negotiation power.