Encyclopedias are a great place to start your research! They often define key terms and give great overviews of topics, and are usually accompanied by a works cited list that you can use to find other relevant resources.
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.
A fascinating resource for anyone interested in theatre, it includes overviews of major concepts, topics and issues, surveys of theatre institutions, countries, and genres, biographical entries on key performers, playwrights, directors, designers, choreographers and composers, and articles by leading professionals on crafts, skills and disciplines including acting, design, directing, lighting, sound and voice.