Summary

Multi-word expressions are linguistic objects formed by two or more words that behave like a ‘unit’ by displaying formal and/or functional idiosyncratic properties with respect to free word combinations. They include an extremely varied set of items (from idioms to collocations, from formulae to sayings) which have been the privileged subject matter of fields such as phraseology, lexicology, lexicography, and computational linguistics. Far from being a marginal phenomenon, multi-word expressions are ubiquitous and pervasive: some estimate that they are as numerous as words in some languages, which makes them as central an issue as words for the understanding of human language. However, their relation with words, and morphology, is by far less explored, not to say neglected, especially in terms of demarcation, competition, and cross-linguistic variation.