As “market referees”, regulators contribute to the delivery of essential public utilities. Their organisational culture, behaviour and governance are important factors in how regulators, and the sectors they oversee, perform. The OECD Performance Assessment Framework for Economic Regulators (PAFER) looks at the institutions, processes and practices that can create an organisational culture of performance and results. The report uses PAFER to assess elements linked to both the internal and external governance of Portugal’s Energy Services Regulatory Authority (ERSE). The review acknowledges the well-respected status of ERSE within the institutional framework, analyses the key drivers of its performance, and identifies a number of challenges and opportunities to help the regulator prepare for the future, including in the context of deep market transformation and the COVID-19 crisis.