The purpose of a literature review is to summarise and synthesise prior research on a topic. It highlights important agreed knowledge as well as any limitations in the research or gaps in understanding. When writing a literature review, you're looking to identify trends or patterns, in addition you could also provide a theory to explain trends or inconsistencies.
The UC Academic Skills Centre runs regular courses on writing in the university context and has prepared this summary on Literature Reviews
The Literature Review: A Few Tips on Conducting it (University of Toronto)
