When, how, and why did the Himalaya become the highest mountains in the world? In 1800, Chimborazo in South America was believed to be the world’s highest mountain, only succeeded by Mount Everest in 1856. Science on the Roof of the World tells the story of this shift, and the scientific, imaginative, and political remaking needed to fit the Himalaya into a new global scientific and environmental order. Lachlan Fleetwood traces untold stories of scientific measurement and collecting, indigenous labour and expertise, and frontier-making to provide the first comprehensive account of the East India Company’s imperial entanglements with the Himalaya. To make the Himalaya knowable and globally comparable, he demonstrates that it was necessary to erase both dependence on indigenous networks and scientific uncertainties, offering an innovative way of understanding science’s global history, and showing how geographical features like mountains can serve as scales for new histories of empire.