As a follow-up on the series of lectures on "Magma & Principles" organized at the EPFL, a book called “ Inservire Domino” has been published under the supervision of the Laboratory of Spatial Manufacturing. Emmanuel Rey has contributed one of the chapters in this publication entitled “Un duo au coeur de l’orchestre”. Written on the basis of recent experience gained by Bauart, the article is an empirical assessment of the key relationship between the architect and his/her clients in the framework of major urban transformation projects. It highlights the complexification but also the enhancement of the role played by the architect in these contexts.