RedLightGreen was a database of bibliographic descriptions on the Web created by Research Libraries Group (RLG).^[1] It used a set of four million records extracted from OCLC's WorldCat database, and was designed to help novice users make selections from the vast bibliographic resources they would encounter in such a large set.^[2] RedLightGreen also allowed users to create citations for works found.

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Work on RedLightGreen began in 2001 with funding from the Andrew W. Mellon Foundation. It was one of the earliest experiments with the Functional Requirements for Bibliographic Records which provides a structured view of bibliographic data.^[3] On July 1, 2006, RLG was merged with OCLC, and it was announced that the RedLightGreen service would be replaced by WorldCat, via Open WorldCat, available at WorldCat.org.^[4]