<p>Energy systems are being reshaped by decarbonisation, decentralisation, electrification, sector coupling, digitalisation, and rising demands for resilience. These developments are changing energy systems from relatively centralised infrastructures into distributed cyber-physical systems that foster increasingly intelligent energy ecosystems. Almost a decade after the process of establishing the journal Energy Informatics began in 2017, the field has reached a level of thematic breadth, methodological maturity, and community identity that makes it timely to clarify its intellectual foundations. Energy Informatics has developed from an emerging research area concerned with digital applications in energy systems into a broader scientific and engineering discipline concerned with the information foundations of digital energy transformation. It is not defined by individual technologies such as data analytics, artificial intelligence, optimisation, smart meters, or digital twins, although these remain important parts of the field. It is concerned with how energy related information is represented, acquired, managed, exchanged, governed, analysed, and used to support the planning, operation, coordination, optimisation, and transformation of energy systems and energy ecosystems. Energy Informatics therefore provides the information centred perspective needed to connect energy engineering, information systems, computer science, software engineering, data science, artificial intelligence, cyber physical systems, energy economics, and sustainability transitions.</p>