Consultant:
- 2005 - 2007: Expert consultant for Constructing Arabic Wordnet in Parallel with an Ontology: This project aims at the development of wordnets for the Arabic languages and is sponsored by the American government and headed by Princeton University. Vossen will be responsible for the European development and coordination.
- 2006: Expert reviewer for the European Union.
- 2002 - 2004: Expert consultant for BalkaNet: the EC-project BalkaNet aims at the development of wordnets for the Balkan languages.
- 2001 - 2002: Expert consultant for EuroTerm: the EC-project EuroTerm aims at the development of domain extension module for wordnets.
- February 2000 - 2002: Expert consultant in the Eagles/Isle project on standardization of multilingual resources for NLP.
- January 2000 - 2003: Expert consultant for Corpus Gesproken Nederlands.
- June 2000: Expert consultant for Van Dale, Groot Woordenboek der Nederlandse Taal, CR-ROM edition
- May 1996 -February 1998: Coordinator of the Dutch-Functional Grammar group in which a group of linguists from the research school IFOTT (now called ACLC), were developing a discourse grammar for Dutch based on Functional Grammar.
- 1993 August - 1995: Expert-consultant in the area of language and information-engineering for the EU (PB/EG nr. C24/10, 28193).
- June 1992 - September 1994: Freelance consultant for Cambridge University Press and Van Dale Lexicography to set up lexical semantic databases.