In January, 2016, in Beijing, Randall Rader, a former Chief Justice of the US Court of Appeals for the Federal Circuit, gave a speech to a private gathering of Chinese Government officials. He had been invited to set out his assessment of China's progress towards the creation of an effective legal system. “The law is the foundation of all prosperity”, he argued. By prosperity he didn't mean only wealth. He included all aspects of a society that underpin its peaceful order and good functioning, including health. Law isn't the first determinant of health that comes to one's mind. Michael Marmot's definitive statement on the social determinants of health—as relevant now as it was in 2008 when first published—focused on early child development, full employment, improved working conditions, stronger health systems, gender biases, and measurement. Legal systems were mentioned in passing as a means to promote equal inclusion. But law was not cited as the foundation for prosperity and health. Public health advocates do not typically see the law as a critical influence on health. They are wrong. Law does not mean only the statutes passed by a legislature. The idea of law is far more important than that. The “rule of law” is a quality of the prevailing political culture, one that puts great weight on notions of good governance, independent accountability, and respect for certain rights. The most basic right of all is the right to liberty. Formally given meaning in Magna Carta (1215), liberty was expressed in this way: “No free man shall be seized or imprisoned, or stripped of his rights or possessions, or outlawed or exiled, or deprived of his standing in any other way, nor will we proceed with force against him, or send others to do so, except by the lawful judgment of his equals or by the law of the land.” But what has this to do with health? The greater the attention societies gave to ideas of liberty, justice, and respect for persons—in other words, to the intrinsic value of individual human beings—the more those societies created the conditions, incentives, and obligations for governments to invest in the value of individual human beings. That value was expressed as commitments to, for example, health, education, and social protection. Global health is one of the most mobilising movements of our times because of its adherence to a transformational trinity of ideas. The first idea is equity—the notion of a fairer world where opportunities and outcomes are more evenly divided among the world's peoples. The second idea is human rights. The Universal Declaration of Human Rights (1948) expressed our common commitment to freedom from want, the dignity of the person, social progress, the right to life, liberty, and the security of the person, the right to an adequate standard of living to provide medical care for one's health and wellbeing, the right to security in the event of sickness, disability, and old age, and the right to social protection, to name only those commitments that are relevant to health. The right to health has since been enshrined in a panoply of official covenants and general comments. The third idea is equally as powerful as equity and rights, but considerably more mysterious—global justice. What is global justice? Here we enter a highly contested space. The history of theories of justice makes any simple definition impossible. But the rule of law is anterior to any of these theories. The rule of law is a largely unacknowledged prerequisite not only for economic growth, but also for a well-functioning health system. The rule of law is identified as a critical element in the quest for sustainable development—SDG 16.3: “promote the rule of law at the national and international levels, and ensure equal access to justice for all.” Next year, the O'Neill Institute for National and Global Health Law at Georgetown University, in partnership with The Lancet, will publish the findings of a Commission on the law's role in advancing health and global justice. The goal of global justice does not have to be an elusive philosophical idea. It can be progressively achieved through attention to an indispensable, although often hidden, determinant of health—law and the rule of law. It's time the health and legal communities joined forces: to make global health and the law one of the most powerful means to achieve global justice.