This is a response I gave to a fantastic question: How much literature review is enough? My reply: First, think of the lit review chapter as being "book-ended" by the introduction (chapter 1) and the methods (chapter 3)– assuming you are doing a standard 5 chapter dissertation. Then the amount of lit review (conceptually) should be the "filler" to tie together chapter 1 and chapter 3. You don’t want to introduce too much in your lit review that does not have direct applicability to your study/research. And whatever you address in the lit review needs to be referenced in the methods and discussion- so you don’t want to include information you can’t really use to explain your methodology or findings. Another way to think of it is like building a house- the intro and lit review become the ground floor/foundation of the house. If you make the foundation really small, the dissertation will be too narrow (not robust enough)- if you make the foundation too big, the dissertation will become mammoth— and what you’re aiming for is a nicely proportioned house. (Sometimes this analogy works for people, sometimes not). I often suggest that you think of the lit review in terms of being persuasive rather than being "fair". Part of the reason that lit reviews become unwieldy is because the writer wants to be ‘fair’ to the literature. I don’t think this is exactly the right approach. A better one would be to ask yourself, "Does including this literature/citation/document make my dissertation more persuasive? Does it really highlight my topic? Does it offer useful information? Does it tie my approach together?"– asking these kinds of questions may help you separate what is critical from what is not. From a purely mechanical point of view, I’d usually include 3-5 citations for each major aspect, and just 1-2 for minor ones. If you have multiple studies saying the same thing, only cite 3-5 of them. You can pick the oldest and the most recent (for example) if you’re trying to show that the literature has been consistent over time. If there are new findings, mention the previous ones, but really focus on the new ones- the dissertation should aim to be reasonably current to what’s happening in the area now. However, if your lit review is more than 2 years old, I’d leave it alone ’til the rest of your dissertation has been drafted. In doing so, you can better tease out what should remain and what should be scrapped.