The article addresses how Britain's major statewide political parties—Labour, the Conservatives, and the Liberal Democrats—adapted to political devolution in Scotland and Wales. It explores party organization, programs, and policymaking. It argues that the Labour Party experienced the most territorial intraparty conflict but fairly rapidly achieved a new balance between British and Scottish/Welsh party interests. The Conservative Party struggled after its 1997 UK election defeat and failed to adapt to multilevel politics with any consistency. The Liberal Democrats experienced the smoothest adjustment, largely on account of their own federal party constitution. The article concludes that the findings provide some backing to “rational choice institutionalist” hypotheses of party change but that a “historical institutionalist” approach can provide a fuller understanding of how parties adapt to devolution reforms.