This page lists resources to help you find collected editions, historical series, and sets & monuments of music, as well as locating individual works within those collections.
An overview of historical editions and an exhaustive list of editions can be found in "Editions, historical" by Sydney Robinson Charles, George R. Hill, Norris L. Stephens, & Julie Woodward in Grove Music Online. (see link below)
The Index to Printed Music (IPM) online indexes individual pieces of music printed in the complete works of composers, in anthologies containing pieces from disparate historical periods, and in other scholarly editions.
Currently IPM contains over 500,000 entries, which also include:
Work lists with listings for volumes in collected editions can be found at the end of articles on composers in Grove Online or The New Grove Dictionary of Music and Musicians in reference at REF ML100.N48 1995.
The classic Historical Sets, Collected Editions, and Monuments of Music : A Guide to Their Contents / compiled by Anna Harriet Heyer is located in reference at REF ML113 .H52 1980.
The print version of IMP is Collected Editions, Historical Series & Sets & Monuments of Music : A Bibliography / George R. Hill, Norris L. Stephens and is available in reference at REF ML113 .H55 1997.
Check publishers' websites to find out if a volume in a composer's collected edition or musical monument series has been published. Below are only a few publishers of collected editions and monuments.