Once the research protocol is completed, Library database searching can begin. This page provides ideas of sources to search but the actual sources to search will vary according to the subject area of your Systematic Review.
For many Systematic Reviews, a search of the large citation databases, such as MEDLINE, the Cochrane Library, Scopus, and Web of Science, is sufficient. A more comprehensive Systematic Review will also search other sources, including a search of the Grey Literature. Note that the Cochrane Handbook, Section 6.2.1 provides guidance on bibliographic databases to search when completing a Systematic Review.1
There are many definitions of grey literature, but it is generally understood to mean literature that is not formally published in sources such as books or journal articles. Conference abstracts for example, are a form of grey literature. See the Library Guide Grey Literature Searching in Health for sources of Grey Literature.