Prevailing frameworks to address planetary environmental challenges tend to focus on setting goals, targets, or boundaries to limit human harm to ecosystems or species. Here we propose an aspirational approach aimed at empowering people to shape a better future for all of life on Earth. We do this by building on the human development approach and its supporting metrics, especially the Human Development Index (HDI), a broadly influential framework that has contributed to decades of human progress by measuring and promoting people’s capabilities to lead the lives that they value. Rather than assessing the state or dynamics of the biosphere, we propose the Nature Relationship Index (NRI), which would focus on measuring the progress of nations towards delivering mutually beneficial relationships among people and the rest of the living world in terms that people widely understand and value. Through an open-ended process informed by expert consultation, international concept testing and indicator development, the NRI could help to incentivize progress towards a world in which humanity thrives together with the rest of life on Earth. We explore the challenges and opportunities of developing a robust NRI and invite broader participation to facilitate this development in collaboration with the United Nations Development Programme Human Development Report.