Scholarly/Critical Edition
Score version selected by an expert who has attempted to determine a composer's intentions about the way a piece was intended to be performed, by examining primary sources, reviewing multiple versions of scores, and applying knowledge of the composer's life and known styles.
Collected Works
One mega-edition of a composer's complete compositions (works)
To find a list online: Grove Music Online (Search by Composer; view "Works")
To find the collected work in the library: M3, alphabetical by composer's last name
Advanced search in the Print Catalog for the composer as the author and complete works as a keyword
Historical Sets
Collections of music according to a region/country or time period, with historical and related focuses
Helpful for lesser-known composers (The Print Catalog sometimes has composers in the notes field, so try a keyword search first on the composer)
In the library: M2, alphabetical by title
Search the Print Catalog by region and by type of music, instrument or genre
Thematic Catalogs
List the numbers assigned by scholars to identify composer's works: e.g., opus numbers, K. numbers (Mozart), etc.
Include the principle theme of each work and information about the score editions