Examining the evolution of the decision-making process in Japan under the Democratic Party of Japan administration between the years 2009-2012, this book offers a multidimensional explanation for the reasons for the DPJ's failure in producing effective policymaking mechanisms. Implementing conceptual tools borrowed from historical institutionalism, the author explains why the Democrats displayed inflexibility in introducing selected elements of the Westminster system, incoherence in regard to many aspects of the decision-making reform, and unwillingness to take advantage of all of the institutional resources at their disposal.