In this article we examine the emerging party systems of the devolved environments, with an eye toward shedding light on the factors that influence the number of parties in a system where parties are already mobilized but the institutional context is new. Our findings demonstrate that electoral rules have an independent effect on the number of parties. More specifically, the use of proportional representation has increased the number of parties. In addition, two social cleavage structure factors appear to affect the design of the party system: class and center– periphery. All of these forces lead to a more complex governing arrangement in the devolved settings than that of the United Kingdom.