Drama for Students is a 30 volume encylopedia Van Wylen has as a part of its eReference collection. It contains essays on over 550 plays and provides summaries and analysis of themes and historical context, as well as bibliographies of additional resources. The easiest way to see if it contains the play you are researching is to do an Advanced Search in Gale Virtual Reference. Enter the play or playwrite in the first search box and "Drama for Students" in the second, and change the dropdown to Publication.
There are also many helpful print reference books, located on the 1st floor of Van Wylen. The are located in the PN1600-3000 section. Here are a few highlights: