The Sustainable Development Goals (SDGs) are an attempt to clarify how best to organize human collectives in a socially and ecologically responsible way. As such, they articulate a notion of ‘planetary health’ that encompasses an ideal of human well-being. Though they build on a long history of developing ways of quantifying the human impact on the earth system, the SDGs provide the most comprehensive set of analytic tools yet developed for this purpose. But, although the metrics are indispensable, the tool-kit also needs something it is so far largely lacking: an analysis of the values underpinning the project. It is missing a clear and compelling presentation of the ethical core of the sustainability project. This is a problem, because if we are not explicit about this aspect of our efforts we risk failing to see opportunities for building consensus around them. This brief article approaches this problem by helping us clarify philosophically why the SDGs matter morally. To that end, two claims are advanced: first, that we must connect the notion of ‘planetary health’ to an explicitly objectivist model of human well-being; second, that we won’t understand the moral point of the SDGs absent a detailed account of this connection.