This article discusses the treatment of collocations in the context of along-term project on the development of multilingual NLP tools. Besides“classical” two-word collocations, we will focus on the case of complexcollocations (3 words or more) for which a recursive design is presented in theform of collocation of collocations. Although comparatively less numerous thantwo-word collocations, the complex collocations pose important challenges forNLP. The article discusses how these collocations are retrieved from corpora,inserted and stored in a lexical database, how the parser uses such knowledgeand what are the advantages offered by a recursive approach to complexcollocations.