Bilingualism, the learning and use of two or more languages, is a linguistic, social, educational and psychological reality for many people and most countries. In the heart of Europe, Belgium, a country with two cultural and linguistic populations, with immigration, international business and institutions, is particularly confronted with this reality. Reaction to and part of its multicultural society, Belgium developed since many years a significant interdisciplinary research activity in the field of bilingualism. The particularity of our study is twofold: First, the research on bilingualism is interdisciplinary, at the crossroad of linguistics, sociology, psychology and educational sciences, each domain presenting its own vectors of publication and communication. Second, while most of the previous studies on the importance of grey literature are citation analyses, our study is based on search results from databases, catalogues, open archives and search engines.