The consortium's review of the state of the art in energy-efficient software, drawing on more than 70 contributors across the partner organisations. A thematic review covers energy measurement, metrics and attribution (wall-plug and PSU measurement, RAPL, modelled and simulated measurement, cloud measurement, tools and benchmarks); AI tooling for code and energy optimisation (small and large language models, mixture-of-experts approaches); sustainable and green AI; sustainable software engineering practices and developer impacts; energy-aware computing; mining, reconfiguration and reconstruction of IT architecture and infrastructure; and standards and certification for green software. A sectorial review then looks at energy-efficient computing for web and SaaS systems, media and gaming, the public sector and mainframe applications. The executive summary consolidates the gaps found across these areas into the research needs GreenCode is addressing, and sets out why the project's contribution is valuable.