The library of the Conservatoire royal de Bruxelles was established at the same time as the rest of the institution in 1832. The first handwritten catalogue, drawn up in July 1835, contains 576 volumes. The first printed catalogue, published in 1870 by Van Lamperen, lists nearly 5,000 works ; as for the four-volume catalogue published by Wotquenne between 1898 and 1912, it contains no less than 16,809 works.

The great wealth of the library collection is thanks principally to the interest in early music which was shared by the first two directors of the Conservatoire, François-Joseph Fétis and François-Auguste Gevaert, along with the work of the librarian Alfred Wotquenne, active bewteen 1894 and 1918.

Amongst the most important historic resources acquired before 1919, there is the Westphal collection, acquired by Fétis in 1840, which manuscripts of Carl Philipp Emanuel Bach and Georg Philipp Telemann. Another important resource is the library of Guido-Richard Wagener, acquired by Wotquenne in 1905 (containing German, French and Italian music of the 17th, 18th and 19th centuries, much of which is contained in volumes which are sumptuously bound).

At present, the collections of the library of the Conservatoire can be estimated to include nearly one million bibliographic items, composed chiefly of scores and books abotu music, but also manuscripts (around 16,500 from before 1850), periodicals (over 1,200 titles), opera libretti (around 8,000 titles), several thousand autograph letters of musicians, iconicographic collections (nearly 10,000 items), concert programmes and all types of recordings.

Alongside the main collections, there are around a hundred special collections, mostly consisting of autograph manuscripts and the archives of composers such as Joseph Jongen, Léon Jongen, Léon Delcroix, René Bernier, Gaston Brenta, Paul Gilson, Henri Thiébaut, Eugène Guillaume, Eva Dell'Acqua or Suzanne Daneau ; great performers like the pianists Arthur De Greef, Camille Gurickx, Hélène Dinsart, Emile Bosquet, violinists Lambert Massart, Alfred Marchot, Laurent Halleux (second violinn of the "Pro Arte" Quartet), Maurice Raskin, the viola player Gilbert Bockstael, the 'cellist Marcel Duwez ; the singers Laure Bergé, Lina Pollard, Gabrielle Wybauw, Germaine Teugels, Nina Philippart ; orchestra conductors Désiré Defauw, Franz André or V.O. Ursmar ; musicologists or critics like Charles Van den Borren, Ernest Closson, Roger Bragard, Maurice Kufferath, Paul Bergmans or Emma Piel ; and amateur musicians such as Docteur Fernand Leroy.

Some of these special collections include documentation which is of great value, and also very specialised: the Docteur J. Hollenfeltz collection is dedicated to Mozart and his son; the Constantin Piron collection is dedicated to French music from the second half of the eighteenth century ; the Alzire Barbier collection consists of popular music from the interwar period ; the Sainte-Gudule collection holds music played during in the Brussels cathedral during the eighteenth century, etc. Lastly, the library also holds a collection in memory of Maria Malibran, donated by the general Wauwermans, along with the Michotte collection which is dedicated to Rossini.

In 2015, the library took back the collection of scores collected by the Belgian Centre for Music Documentation (CeBeDeM), in line with that organisation's aim to help promote Belgian contemporary music both in Belgium and abroad.