The Grey Matters resource is a free online tool for finding health-related grey literature that is not published commercially and may be inaccessible via bibliographic databases.

The System for Information on Grey Literature in Europe used to give open access to 700.000 bibliographical references of grey literature (paper) produced in Europe and allowed to export records and locate the documents.

Examples of grey (gray) literature include technical or research reports, doctoral dissertations, some conference papers, some official publications, and other types of grey literature.