The coffered dome designed by Philibert de L’Orme (1514–70) for the chapel of the Château d’Anet in northern France between 1549 and 1552 is a masterpiece of stereotomy — the stone vaulting technique characterised by the custom cutting (or dressing) of a vault’s components or voussoirs. The dome was executed by first individually dressing its large voussoirs, so that they would fit one another precisely, and then dry assembling them like the pieces of a three-dimensional jigsaw puzzle. The spiralling ribs that form the coffers added a layer of complexity to the work, for they are embedded in the voussoirs; thus the exact shape and position of the rib sections belonging to each voussoir had to be calculated precisely before dressing to ensure that, after assembling, they would form the correct pattern over the vault’s surface. The dome’s execution method continues to baffle historians, in particular with regard to the transfer of the complex pattern formed by the ribs on to the templates used by the stonecutters to shape the voussoirs. Based on a new 3D laser scan of the dome and on the analysis of late medieval and early modern stereotomic practices and theories, this article offers a new interpretation of the methods that de L’Orme adopted at Anet and of their significance within the panorama of sixteenth-century architectural practice and theory.