Most teaching and reference materials on English idioms are primarily intuition based. As such, they often include seldom-used idioms and incorrect descriptions of the meaning and use of some idioms, hence limiting their usefulness to ESOL students. This article demonstrates how this problem can be addressed through a corpus-based study of the spoken American English idioms used most frequently by college and other professional ESOL students learning American English. The study involved a close concordance search and analysis of the idioms used in three contemporary spoken American English corpora: Corpus of Spoken, Professional American English (Barlow, 2000); Michigan Corpus of Academic Spoken English (Simpson, Briggs, Ovens, & Swales, 2002), and Spoken American Media English (Liu, 2002). According to the search results, four lists of the most frequently used idioms were compiled, with one based on the overall data and the other three on one of the corpora. The study uncovered interesting English idiom use patterns. The results were compared with information in nine major current idiom dictionaries, which revealed inadequacies of the existing idiom teaching and reference materials in terms of item selection, meaning and use explanation, and the appropriateness of the examples provided. The article discusses pedagogical and research implications, including suggestions for improving the development of idiom teaching and reference materials. (Contains 3 footnotes and 3 tables.)