Grey Literature is literature that has not been published or has been published in non-conventional forms. Grey Literature can include health reports, minutes, data-sets, photographic evidence and trials. Grey Literature is very useful to find raw data.
Much Grey Literature can be found through search engines such as Google or by going to specific websites.This link offers really good tips on how to search the web effectively.
Open Grey offers a searching interface for Grey Literature produced in Europe.
The links below offer suggestions for specific institutions which produce Grey Literature.