Zero emission vehicles (ZEV) and plug-in electric vehicles (PEV) are critical technologies to attain deep reductions in greenhouse gases from transportation. PEV markets, however, have grown more slowly than anticipated by many observers. In this study, we seek a deeper understanding of the challenges facing PEV markets and how they might evolve in different regions. Using a Technology Innovation Systems (TIS) framework, we examine the major conditions—political, technological, economic, and societal—that drive the development, deployment and use of these vehicles at the state level. With this holistic approach, we identify strengths and weakness of the innovation systems in a few representative states, which we translate into recommendations for policy strategy. We find that while significant efforts have been undertaken to support PEV innovation, there are significant deterrents to the broader market uptake of PEV.