Background: Health systems frequently consume considerable amounts of energy and resources, and generate large and multifaceted waste and pollution streams. Improving their own environmental sustainability may provide benefits and opportunities. Sustainability initiatives and activities in health systems tend to be bottomup, local and driven by providers, which results in challenges for transferability and scaling-up. Local context: The National Health Service (NHS) is the publicly funded health-care system for the United Kingdom. It employs more than 1.7 million people and caters to a population of 65.1 million. Within its decentralized structure, several providers and trusts had been engaging in a variety of smallscale, independent and locally-coordinated sustainability initiatives. Approach: The Sustainable Development Unit (SDU) was established in 2008 to work with and support the NHS to be more environmentally and socially sustainable, thus contributing to its overall financial sustainability. Thereafter, strategies were developed; governance structures and mechanisms for sustainability were put in place; stakeholder engagement mechanisms were implemented; and supporting mechanisms were devised. Relevant changes: Information and indicators relevant for sustainability have been routinely collected since the SDU’s establishment, and net comparative gains have been observed in reduced use of resources, reduced carbon footprint, reduced waste generation and stakeholder engagement. Lessons learnt: some aspects of the NHS experience may be transferable to other national health systems. These include the importance of manageable entry points and stakeholder engagement, how to promote change, the complementarity of top-down and bottom-up action, and the inextricability of the environmental, social and economic dimensions of sustainability in health systems.