This paper explores both the promise and the possible pitfalls of the plug-in hybrid electric vehicles (PHEV) and vehicle-to-grid (V2G) concept, focusing first on its definition and then on its technical state-of-the-art. More originally, the paper assesses significant, though often overlooked, social barriers to the wider use of PHEVs (a likely precursor to V2G) and implementation of a V2G transition. The article disputes the idea that the only important barriers facing the greater use of PHEVs and V2G systems are technical. Instead, it provides a broader assessment situating such "technical" barriers alongside more subtle impediments relating to social and cultural values, business practices, and political interests. The history of other energy transitions, and more specifically the history of renewable energy technologies, implies that these "socio-technical" obstacles may be just as important to any V2G transition-and perhaps even more difficult to overcome. Analogously, the article illuminates the policy implications of such barriers, emphasizing what policymakers need to achieve a transition to a V2G and PHEV world. (C) 2008 Elsevier Ltd. All rights reserved.