Every language contains idiomatic expressions. In spite of their widespread occurrence, their linguistic properties have so far not been deeply and systematically investigated. The aim of this project is to increase our understanding of ‘the language of idioms’ by focusing on their behavior in syntax. Therefore, the main research question is: What is the syntax of idioms? This question can be naturally divided into two sub-questions, which correspond to two sub- projects: (i) What is the internal syntax of idioms, i.e. what characterizes their internal organization and makeup?; (ii) what is the external syntax of idioms, i.e. how does material contained within the idiom interact with material that is not part of the idiom? Subproject 1 aims to show that idioms, in spite of their superficially ‘special’ appearance, are built up by the very same syntactic and morphological structure building mechanisms that are responsible for non-idiomatic expressions. Subproject 2 aims to show that idiomatic expressions are essentially opaque domains, but that dependencies with idiom-external material is possible under certain narrowly defined circumstances. The empirical basis for our investigation into the syntax of idioms will consist of idioms from non-standard varieties of Dutch. On the basis of dialect grammars and dictionaries, and also on the basis of additional fieldwork, an electronic database will be developed which will serve as a tool for our systematic investigation into the syntax of idioms.