In 2011 an international working group developed a vocabulary of types of grey literature (henceforth GL Vocabulary). The typology of grey literature is an RDF (Resource Description Framework) vocabulary expressed in a SKOS (Simple Knowledge Organisation System) concept scheme. Each type is provided with a definition and most of them are accompanied by a prototypical example of a document for which it can be used. The GL Vocabulary is published as linked data. Each type is identified by a URI and the vocabulary is interlinked and mapped to other datasets. The GL Vocabulary is distributed as a controlled vocabulary in machine-readable format. More information can be found on the project web pages: http://code.google.com/p/grey-literature-typology/ and in the GL13 Conference Proceedings "A linked-data vocabulary of grey literature document types: Version 1.0" http://invenio.nusl.cz/record/81435?ln=en.