The word Theatre is often spelled as Theater. Watch for variant spellings of this term. It could affect search results.
Subject Searches are based on Library of Congress Subject Headings. They are usually more precise than keyword searches.
The World Catalog is a huge database representing holdings of libraries across the United States and some countries abroad. Many of these holdings, especially books, are available for loan through Interlibrary Loan.
Electronic books in the Boreham Library on theatre and drama are available at this link. More specific topics can be searched individually.