These books, along with many other titles, can be found in the Reference section of the Library. Click on the title to go the record in the Library Online Catalog. Be sure to check the circulating collection for books you can check out, too.
Oxford Encyclopedia of British Literature by 
The Cambridge guide to literature in English 3rd ed. / edited by Dominic Head. by 
The Oxford Companion to Chaucer by 
The Oxford companion to English literature 7th ed. / edited by Dinah Birch. by 
The Oxford companion to twentieth-century literature in English by 
The Oxford Companion to Shakespeare by These databases will be useful to you in your research:
