Despite decades of energy efficiency (EE) policies, energy consumption in places like Europe has barely peaked, warranting research on policy implementation. This thesis relies on participatory research within a Swiss regional, utility-led energy efficiency programme (EEP). It explores the impact and monitoring logics of the EEP, as illustrative of transition intermediaries – i.e. actors facilitating and amplifying the actions of others. Calculated electricity savings, a flagship impact indicator, appear as a low-precision proxy of metered savings, particularly compared to simpler deemed savings. Further observations call into question this quantification-based monitoring, as it narrows intervention options to EE measure implementation support in a top-down, incremental approach. It is seen as a guarantee of programme credibility but leads to a bias towards technical staff profiles while increasing operational burden and disempowering recipients. A discursive analysis shows that alternatives tend to be associated to this spare paradigm, hindering the emergence of more transformative (i.e. systemic, bottom-up) approaches. A more comprehensive monitoring framework is thus proposed, considering, beyond (a) support, (b) network and (c) mobilization activities and drawing attention to the differentiated requirements along activity lifecycle phases: (i) development, (ii) launch, (iii) cruise, (iv) transfer, and (v) fruition.