Since the time of Cavaille-Coll, the grand organs of the Cathedral of Notre-Dame and the parish church of Saint-Sulpice, Paris, have enjoyed steady international recognition and attention. This is due not only to their status as Cavaille-Coll's two largest creations and among his most famous opera but also for the subsequent tonal and mechanical changes made to them over the years by their titulaires and restorers. Although both instruments were comparable in size and completed within six years of each other, various installation peculiarities and Cavaille-Coll's ever-evolving style produced two rather different instruments whose tonal paths have diverged yet more ever since. The organ in Saint-Sulpice, of which the majority of tonal resources, mechanisms, and chests are still as they were in 1862, has escaped significant invasive overhaul. In contrast, since its completion in 1868, the Notre-Dame organ has undergone radical alteration more than once and now stands as a monument as much to modern technological progress as to its various builders. This oblique divergence between the two organs is largely the result of changes made to the Notre-Dame organ by titulaires Louis Vierne and Pierre Cochereau. However, the modern-day use of these organs also represents important differences between the two. The Notre-Dame organ is now capable of playing literature from all eras of organ music, yet improvisation is the most performed genre on this organ. In contrast, the organ at Saint-Sulpice is better suited to playing French music, yet it is on this organ that the music of German composers such as Bach and Mendelssohn is also regularly played. Social matters are also of interest. "Decorum" and guarded admission were de rigueur at Saint-Sulpice during the tenures of Charles-Marie Widor and Marcel Dupre. Such intense social consciousness was not so strict at Notre-Dame. In contrast, today the Saint-Sulpice organ is a weekly host to numerous tourists, but that of Notre-Dame is virtually inaccessible to the unannounced visitor. Finally, although alterations are necessarily shaped by the personalities involved, other factors such as architecture and even the weather have also played important roles in the daily use of these instruments.