A searchable online collection of encyclopedias, dictionaries, atlases, biographies, language dictionaries, and other reference titles.
Use sites from universities or colleges by typing in "site:.edu" before your search. For example: site:.edu modern drama brecht.
In addition to searching for your playwright in the library catalog, here are some books you could possible use.
The Columbia Encyclopedia of Modern Drama by 
Modern Drama and the Rhetoric of Theater by 
