Two experiments examined the nature of access, storage, and comprehension of idiomatic phrases. In both studies a Phrase Classification Task was utilized. In this, reaction times to determine whether or not word strings constituted acceptable English phrases were measured. Classification times were significantly faster to idiom than to matched control phrases. This effect held under conditions involving different categories of idioms, different transitional probabilities among words in the phrases, and different levels of awareness of the presence of idioms in the materials. The data support a Lexical Representation Hypothesis for the processing of idioms.Investigation of the processes underlying sentence comprehension has tended, understandably enough, to consider the more simple cases which confront the listener. For example, examinations of lexical processing during sentence comprehension have typically employed words with straightforward and easily derived interpretations. While an important exception to this rule is the study of lexical ambiguities, even this work deals with words which possess relatively well-defined literal meanings. There is, however, a large class of items--including idioms, metaphors, and proverbs--which are extraordinarily common in the language but which have been largely ignored in comprehension research; the few attempts to discover how the compre- hension device computes nonliteral meanings for these items have found them to be remarkably intractable. The high frequency of occurrence ofnonliteral materials alone necessitates that the processes responsible for their comprehension be incorporated in any complete comprehension model. Idioms, in particular, present an important challenge to those interested in building a performance model for sentence comprehension, and the purpose of this paper is to examine some of the basic aspects of how we come to understand idiomatic expressions. In order to see the nature of the problems that idioms raise for the comprehension device it is first necessary to consider exactly what constitutes an idiom. In its simplest form an idiom is a string of two or more words for which meaning is not derived from the meanings of the individual words comprising that string. Thus, the idiomatic meaning of "kick the bucket" has little to do with the meanings of either "kick" or "bucket"; similarly, the meaning of "by and large" has little to do with the meanings of either "large" or "by."Thus, by and large, idioms defy traditional concepts of syntactic and semantic analysis,