Syntactic constructions may form an alternative to, or compete with the morphological expression of semantic and grammatical content. This applies to the passive forms of verbs, the progressive form, analytic causatives, adjective-noun sequences, and particle verbs in Dutch. In this article I develop a view of the Dutch lexicon in which this interaction between syntax and morphology can be understood. The central notion used is that of the constructional idiom, a construction with a (partially) non-compositional meaning, of which not all terminal elements are fixed. These constructional idioms, like morphological word formation, serve to extend the fund of expressions that are available for concatenation in the syntax.I would like to thank the anonymous referees of this journal, and Farrell Ackerman, Arie Verhagen, and the audience at the MMM3 meeting in Barcelona, September 2001, for their comments on previous drafts of this paper.