Academic and policy literatures are seeing a growing discussion about ‘clean energy disruption’. However, the term disruption often lacks definitional clarity. Departing from the concept of disruptive innovation and based on a review of firm-based management and socio-technical transitions literatures, we derive four dimensions of system disruption: technology, markets and business models, ownership and actors, and regulation. We apply these dimensions to analyse the status of disruption in two exemplary countries pursuing ambitious low-carbon energy transitions: Germany and the United Kingdom (UK). The views of a diverse range of actors are investigated regarding how disruption is unfolding and what is seen as disruptive in the energy sector. Our analysis draws on 28 expert interviews, supplemented with a review of empirical studies. We find that despite comparable shares of renewables in the two countries' electricity systems, the scale of disruption in Germany significantly exceeds that in the UK, covering all four rather than just two dimensions. We also find a greater awareness of and resistance to expected further waves of disruption in Germany, as compared to the UK. Finally, we discuss the implications of the notion of disruption for understanding and governing socio-technical transitions.