Abstract The language of systems can be highly useful when defined clearly. It can help make sense of the interconnectedness of key actors, the ‘emergence’ of outcomes from large numbers of interactions, and the proposed transformation – by many governments - towards sustainable energy systems. However, ‘whole systems analysis’ and ‘systems thinking’ is often too vague to guide this project well. To explore these issues in depth, we show how they arise frequently in UK energy policy research and its impact on policymaking. First, our systematic review shows how researchers present patchy or inconsistent stories, in which the role of policy and policymaking is unclear, when they describe energy systems. Second, UK and devolved governments often use the language of systems to propose paradigmatic energy policy change, but refer to a metaphor rather than academic insights. Third, we outline three ways to make clearer sense of energy transitions and policy with reference to socio-technical, complex, and social-ecological systems.