A literature review surveys scholarly articles, books, dissertations, and conference proceedings relevant to your research problem, providing a description, summary, and critical evaluation of each work.
Purpose of the literature review:
Three important things to know about research
Nearly every scholarly research article begins with a brief, basic review of existing literature. This review introduces the subject being investigated and what is already known about it, in order to provide context for the author's new research.
Check the "Introduction" section of this original research article for an example:
There is also a whole category of scholarly articles known as literature reviews. (Generally, these will use words like "Literature Review," "Review," or "Review of the Literature" right in the title.) These articles do not conduct new research, but only review existing research on some subject, in order to summarize the current state of knowledge and help other researchers exploring the same topic.
An example of a Literature Review article:
If you have any of these questions
How far back should you look?
How many sources should you have?
What kinds of sources should you use?
Ask your instructor! Different departments have different requirements.