These kinds of reference books provide essay-length overviews that address major issues and topics within a field of study. The authors not only discuss key content but they also provide a more sophisticated level of analysis and contextualization than you might find in a textbook or introductory study. The authors are chosen for their research in specific areas and deliver authoritative essays. The material they choose to include in their bibliographies are good points of departure for further research and reading.
Literature reviews, are a useful tool when doing research. They are a kind of writing, generally published in journals, that focuses on the issues involved in a particular research question and the debates and developments among scholars. They map out the intellectual landscape succinctly and give you the major landmarks in terms of key authors and significant articles and books for further reading.
Doctoral students go through an exhaustive literature search when writing their dissertations. They also tend to work on new questions, sometimes ones that have received very little attention from scholars before. You can obtain many of these dissertations and benefit from all the bibliographic treasues and new ideas. Check ProQuest Dissertations & Theses to identify dissertations on your topic.