A literature review is essentially a summary of the research that has been done in your field. A literature review can be used to argue or support a claim, or it may simply be used as background information. If you are writing a paper where you need to argue or support a claim using evidence from previous research, then you should write a critical literature review. This type of review will focus on the current state of knowledge within your field, and how this knowledge contributes to your own argument/claim.