The Library Catalog allows you to search for physical materials in the collections (like books and audiovisual recordings), but also provides access to journal and newspaper articles, book chapters, reviews, and more by simultaneously searching a wide variety of open access repositories and many (but not all) of the subscription databases provided by the Heard Libraries. You can learn more about the Library Catalog here.
There are several subject-specific databases that will help you with your research on Wagner and his operas. The content found in RILM and Oxford Music Online are not included in the library catalog search, so you need to search them separately using the links below. Much of the content from the Music Periodicals Database is in the catalog, but it's often easier to search in the ProQuest interface.