The competitive federalist system facilitated state leadership and the diffusion of innovative policies that addressed climate change and energy issues in the absence of comprehensive federal action at the start of the twenty-first century. In a competitive federalist system state governments and their politicians challenge one another horizontally and the federal government vertically for legislative credit and functional authority on relevant policy issues. What drove state-level climate and clean energy leadership from 2001 to 2012? This dissertation develops three competitive federalism-based hypotheses for analysis: (H1) A national, bipartisan network of ambitious, entrepreneurial governors drove climate and clean energy policy innovation from 2001 to 2012; (H2) the State Energy Program Recovery Act resources reduced the policy adoption gap between early enactors and laggards in clean energy financing and regulation; (H3) and justification for climate and clean energy activities in the states shifted from environmental to economic rationales from 2001 to 2012 (Figure ES1). While competitive federalism theory has centered on both fiscal and ideological considerations driving innovation in the policy environment, the experience of climate change policymaking and clean energy actions at the state level during the period under consideration reveals a clear partisan divide in policymaking within this domain.