Abstract: Idioms are parts of the lexicon, representing a significant aspect of language behavior. Examination of their behavior as fixed expressions has proved that the y have internal linguistic structures. The authors also find that idioms do not only have structures, but the structure is also related to that of their non-i diomatic or actual meaning. This leads to a division between transparent idioms , whose syntactic structure is the same as its non-idiomatic meaning, and opa que idioms, whose structure is disjoint from that of its non-idiomatic meanin g. We discover that an idiom can behave syntactically only in ways that its lite ral counterpart does. This is by no means a complete picture of idioms and there is still much to be learned. Idiomatic language is remarkably complex and each phrase demands its own analysis in terms of its syntactic, semantic, pragmatic , and conceptual properties. The study of idioms can reveal more about the natu re of fixed expressions, figurative language, and finally, of language itself .