Important basic sources
Oxford Music Online includes substantial articles authored by scholars, excellent works lists and bibliographies. Check the "F: Studies of the Works" ("ii. Orchestral music") and "J. Other studies" sections of the Bibliography to find important books and articles specifically on this composition.
Kinsky, Georg. Das Werk Beethovens ; thematisch-bibliographisches Verzeichnis seiner sämtlichen vollendeten Kompositionen. München : G. Henle Verlag, [©1955].
*Dorfmüller, Kurt. Ludwig van Beethoven : thematisch-bibliographisches Werkverzeichnis. München: G. Henle Verlag, [2014].
2 volumes.
Gesamtausgabe:
Beethoven, Ludwig van. Werke. München : G. Henle, 1961.
There are numerous references to the Eroica in the text of this Grove Music Online article and bibliographical references to books/articles about this musical work in the bibliography at the end of the Grove article. Check the "F: Studies of the Works (ii. Orchestral music" and "J. Other studies" sections of the Bibliography to find important books and articles specifically on this composition.
2. Search the Vassar Libraries' Online Catalog for books, particularly those listed in the Grove article's bibliography. If Vassar does not own them, try Interlibrary loan. If no call number appears for a book you would like and the status "1 copy being processed for Mus Book" is displayed, ask at the Music Library Circulation Desk.
By subject: "Beethoven Ludwig Van 1770 1827 Symphonies No 3 Op 55 E Major" to find books about the composition such as:
Sipe, Thomas. Beethoven, Eroica Symphony. Cambridge ; New York : Cambridge University Press, 1998.
By keyword: “Beethoven Eroica" and "Beethoven Symphonies No 3", modify your search by "printed material" to quickly search the contents notes of chapters of books that may be relevant:
ML410.B4 B2812 2000 (online and in-print versions)
Beethoven and his world. Princeton, N.J. : Princeton University Press, ©2000--
3. Check these databases for articles, particularly those listed in the Grove article's bibliography. Music Periodical Index and JSTOR provide many full text articles. RILM Abstracts cites additional scholarly articles, but has only abstracts and no full text.
RILM Abstracts of Music Literature (1967-current)
Abstracts only, no full text, for items from 1967-present. RILM indexes more scholarly publications and is interdisciplinary in coverage. Indexes music periodicals, chapters of books, festchrifts and periodicals in related subjects.
Advanced search most useful. Allows for browsing types of documents, instruments, etc. to add to your search query.
To find full text of articles: check in Music Periodicals Database or JSTOR to see if either database contains the full text or check Vassar Libraries' Online Catalog to see if Vassar owns the print. If Vassar does not own the periodical, try Interlibrary loan.
Music Periodicals Database (Full-Text)
Full text for many--not all--articles. Indexes music periodicals only. Although there is overlap with RILM Abstracts, tends to cover the less scholarly, more popular titles.
JSTOR is not an index, but may be used to search texts of those 112 music journals that appear in JSTOR. JSTOR seems like an index for the journals it covers since it can be searched by keyword, but it does not allow you to search by subject.