Collected editions provide authoritative, scholarly publications of music that have been edited and researched by experts. These multi-volume editions are useful to scholars and performers alike because they are based on research of the original manuscript and print sources; they also often contain essays with much information about the history of the pieces contained, the extant sources, and performance practice of the composer's time.
Collected editions generally fall into two types: editions of the complete works of an individual composer (call numbers starting with M3); and editions of music by various composers, grouped by time period, nationality/region, or instrument (call numbers starting with M2). Examples of each are below:
Series: Recent Researches in Music of the Nineteenth and Early Twentieth Centuries
Le Tresor des Pianistes by 
Wydanie narodowe dzieł Fryderyka Chopina = National Edition of the Works of Fryderyk Chopin by 
Neue Ausgabe sämtlicher Werke = New edition of the complete works by 
Sämtliche Lieder für Singstimme und Klavier (Complete Songs for Voice and Piano) by 
New Edition of the Complete Works = Novoe polnoe sobranie sochineniĭ by It can be challenging to locate individual compositions within multi-volume collected works editions, or to find scholarly editions for more obscure composers. Below are several published indexes that can help you locate a work within a collected edition:
Historical Sets, Collected Editions, and Monuments of Music by 
Collected Editions, Historical Series and Sets, and Monuments of Music by 