Subject Encyclopedias are scholarly works written by experts on a variety of topics. The articles are typically longer and more detailed than general encyclopedias. The background information provides a good starting point as you begin the research process. Here are some of the ways a subject encyclopedia can help guide you:
Encyclopedia of Asian Theatre by 
Encyclopedia of Latin American Theater by 
Encyclopedia of Musical Theater by 
The Oxford companion to theatre and performance This ebook covers styles and movements, organizations, regions and traditions. It has a strong focus on biographies of actors, playwrights, directors, and designers.
The Oxford companion to American theatre A guide to the American stage from its beginnings to the present. Includes entries on playwrights, plays, actors, directors, producers, songwriters, famous playhouses, dramatic movements, classic works, commercially successful plays, and foreign figures that have influenced American dramatic development.
The Oxford companion to Shakespeare Provides a guide to Shakespeare's plays and poems, and their interpretation around the world over the last four centuries. Covers topics from the conjectured identity of the Dark Lady of the Sonnets to the misprints in the First Folio, from Shakespeare's favorite figures of speech to the staging of Othello in South Africa.
New Oxford Shakespeare Presents an entirely new consideration of all of Shakespeare's works, edited from first principles from the base-texts themselves, and drawing on the latest textual and theatrical scholarship.
Sage provides online Encyclopedias, Handbooks and Dictionaries that cover topics in the Social Sciences.
Gale Virtual Reference Library includes the full text of over 100 subject encyclopedias spanning multiple disciplines.
