The Library's print collection includes many plays in individual volumes, and many more that are published in collections, or anthologies.
To find a specific play use the "Books" option in the library search box to enter the play title, placing quotes around the title, e.g. "raisin in the sun." This will find that title in a stand-alone edition or as part of an anthology. You might also find critical works about the play.
If you don't find the play you need in the catalog try Play Index AND Inter-Play listed to the right. The catalog records for some anthologies don't include detailed title information but you can find the titles through Play Index or Inter-Play.
These volumes are found on the first floor of the library, near the reference desk
Encyclopedia of Musical Theatre 782.14 G15e2001
Oxford Encyclopedia of Theatre and Performance 792.03 Ox2k
A Chronology of American Musical Theater 782.14 N82c
New York Times Guide to Arts of the 20th Century 700.904 N42b