The reference collection is a great place to begin your research. These short relevant articles will give the basic understanding you need to formulate a good research question.
"... a comprehensive survey of the latest research--as well as the foundational teachings--in this broad field. Featuring 150 original, signed articles by leading scholars from many different fields of study it brings together knowledge from classics, philosophy, literature, literary theory, cultural studies, speech and communications." (publisher's website)
"This is the most wide-ranging and up-to-date dictionary of critical theory available, covering the whole range of critical theory, including the Frankfurt school, cultural materialism, gender studies, literary theory, hermeneutics, historical materialism, and sociopolitical critical theory."
"... explores the evolution of the Public Relations field, with examples from history describing events, changing practices, and the key figures who developed and expanded the profession."