Grey literature is generally material and research produced by organizations outside of the traditional commercial or academic publishing and distribution channels. For the health sciences grey literature can include government documents, clinical trials, dissertations, theses, materials in open depositories, and web pages. Organizations that produce grey literature can include government departments and agencies, non-governmental agencies, academic centers and departments, hospitals, associations or researchers.
It may be difficult to discover, access or evaluation grey literature since grey literature may be made available to the public or may only be distributed privately within an organization or group.
NDLTD - The Networked Digital Library of Theses and DIssertations is an International organization promoting the adoption, creation, use, dissemination, and preservation of electronic theses and dissertations. The Global ETD search engine is where you can search these resources.