The rule of ecological law is a fitting complement to degrowth. Planetary boundaries of safe operating space for humanity, along with complementary measures and principles, provide scientific and ethical foundations of the rule of ecological law, which should have several reinforcing features. First, it should recognize humans are part of Earth’s life systems. Second, ecological limits must have primacy over social and economic regimes. Third, the rule of ecological law must permeate all areas of law. Fourth, it should focus on radically reducing material and energy throughput. Fifth, it must be global, but distributed, using the principle of subsidiarity. Sixth, it must ensure fair sharing of resources among present and future generations of humans and other life. Seventh, it must be binding and supranational, with supremacy over sub-global legal regimes as necessary. Eighth, it requires a greatly expanded program of research and monitoring. Ninth, it requires precaution about crossing global ecological boundaries. Tenth, it must be adaptive. Although the transition from a growth-insistent economy headed toward ecological collapse to an economy based on the rule of ecological law is elusive, the European Union may be a useful structural model.