Though several organs were installed in the cathedral over time, the earliest ones were inadequate for the building. The first noteworthy organ was finished in the 18th century by the noted builder François-Henri Clicquot. Some of Clicquot's original pipework in the pedal division continues to sound from the organ today. The organ was almost completely rebuilt and expanded in the 19th century by Aristide Cavaillé-Coll.
The position of titular organist ("head" or "chief" organist) at Notre-Dame is considered one of the most prestigious organist posts in France, along with the post of titular organist of Saint Sulpice in Paris, Cavaillé-Coll's largest instrument.
The organ has 7,800 pipes, with 900 classified as historical. It has 111 stops, five 56-key manuals and a 32-key pedalboard. In December 1992, a two year restoration of the organ was completed that fully computerized the organ under three LANs (Local Area Networks). The restoration also included a number of additions, notably two further horizontal reed stops en chamade in the Cavaille-Coll style. The Notre Dame organ is therefore unique in France in having five fully independent reed stops en chamade.
Among the best-known organists at Notre Dame was Louis Vierne, who held this position from 1900 to 1937. Under his tenure, the Cavaillé-Coll organ was modified in its tonal character, notably in 1902 and 1932.
Léonce de Saint-Martin held the post between 1932 and 1954. Pierre Cochereau initiated further alterations (many of which were already planned by Louis Vierne), including the electrification of the action between 1959 and 1963. The original Cavaillé-Coll console, (which is now located near the organ loft), was replaced by a new console in Anglo-American style and the addition of further stops between 1965 and 1972, notably in the pedal division, the recomposition of the mixture stops, a 32' plenum in the Neo-Baroque style on the Solo manual, and finally the adding of three horizontal reed stops "en chamade" in the Spanish style.
After Cochereau's sudden death in 1984, four new titular organists were appointed at Notre Dame in 1985: Jean-Pierre Leguay Olivier Latry, Yves Devernay (who died in 1990), and Philippe Lefebvre This was reminiscent of the 18th-century practice of the cathedral having four titular organists, each one playing for three months of the year.
There are five bells at Notre Dame. The great bourdon bell, Emmanuel, is located in the South Tower, weighs just over 13 tons, and is tolled to mark the hours of the day and for various occasions and services, ringing in a resounding. This bell is always rung first, at least 5 seconds before the rest. There are four additional bells on wheels in the North Tower, which are swing chimed. These bells are rung for various services and festivals. The bells were once rung manually, but are currently rung by electric motors. When it was discovered that the size of the bells could cause the entire building to vibrate, threatening its structural integrity, they were taken out of use. The bells also have external hammers for tune playing from a small clavier.
In the night of 24 August 1944, as the Île de la Cité was taken by an advance column of French and Allied armoured troops and elements of the Resistance, it was the tolling of the Emmanuel that announced to the city that its liberation was under way.
In 2012 as part of a huge project the 4 old bells of the North tower have been removed melted down and recast into a new set of 8 bells and are due to be rehung in early 2013 back in the North tower. A 9th Bell called Marie is also being cast and will hang with Emmanuel in the South tower.