The principle of ‘Do No Environmental Harm’ is becoming an essential standard in humanitarian action. As the impacts of climate change and environmental degradation intensify, humanitarian organisations must not only respond to immediate needs but also ensure that their interventions do not further harm the environment or the communities they aim to assist. Integrating environmental considerations is essential for safeguarding livelihoods, strengthening resilience, and supporting sustainable recovery. This paper explores how the principle of ‘Do No Environmental Harm’ builds on the broader ethical foundation of ‘Do No Harm’, why greening humanitarian action is urgent, and how humanitarian considerations can be embedded into humanitarian operations. (From the report abstract.)