Q. Where can I find opera librettos?

There is no single place to look for opera librettos.  Some places you might try include the following:

1. Browsing the Operas-Librettos subject heading in the catalog.  This tends to be the books in reference that include the librettos for entire genres or composers (sometimes not all works will be included.)
2. Search the library catalog for [Name of Opera] and librett* but do not limit to score.  Librettos that are published separately from the score are considered books.
3. Consult the critical edition for scholarly material (M3, alphabetical by composer).
4. For librettos of last resort, you might try looking at a CD liner notes for the entire work.  These are not the most reliable resource and should only be used if the other options have not succeeded.