A long-span glass roof covers the public space at the Ernst & Young’s new headquarters in Luxembourg. This light-weight steel grid shell is extremely shallow and still works well due to a set of highly tensioned horizontal cables which not only take the horizontal thrust of the shell but also stiffen it through slender posts which connect them to the shell. The novel roof is the result of an intense and fruitful collaboration between architects and engineers. The conceptual and structural design, fabrication and erection of the structure are presented in this paper.