Gray Literature and Technical Reports

Charles R 1994. Information sources in grey literature. 3rd ed. London Bowker Saur. Good overview of gray literature. 

Godfrey, L. E. and H. Redman. 1973. Dictionary of Report Series Codes, 2nd ed. New York Special Libraries Association. Older but still useful, the dictionary provides a listing of report initials and numbers to research conducted by numerous agencies that contracted with the U.S. government after World War II. 

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