If you are looking for a specific play, first try searching by title and author in a WorldCat advanced search. If the play script was published as a book, it should be easy to find in this way. Many plays published in anthologies can also be found through a title / author search. If not, try searching by keyword or searching for the title of the anthology.
To find all plays by a particular playwright, search by author.
Subject headings can be useful if you are searching for plays on a certain theme or in a particular category. Start with a keyword or title / author search and then browse through subjects within descriptions in the WorldCat record.
Limiting your search to books will help you filter out items such as DVDs from your search results.
Sorting your search by Best Match (rather than by Library) will help you to discover plays that we don't have at Bertrand.