A literature review looks at key published material (scholarly articles, books, pamphlets, etc.) on a particular issue, area of research, or theory and provides not only a summary of the source, but also a critical evaluation. Each source is summarized, synthesized, and often evaluated. More than a mere summary of the sources, it highlights what is and is not known, identifies controversy surrounding a topic, formulates questions that need further research, linking the known literature to how your research adds to the larger field of study.
A literature review can be part of a larger research project in which the researcher presents a proposal, plan of action, or primary research work (a survey, interviews); or, it can stand alone as an analysis of what the experts say on a given issue or area.
For a quick overview, watch this excellent video: What is a Literature Review? by Steely Libraries NKU.
A literature review: