Over the last 20 years vocabulary research has grown from a Cinderella subject in foreign language teaching and research to a position of some importance. Vocabulary is now considered integral to just about every aspect of language knowledge. With this development have come standard and widely-used tests, such as vocabulary size and lexical richness measures, and very commonly accepted metaphors, such as the mental lexicon as a web of words. Less widely known outside academic circles, however, is the extensive work on learners` lexis and the utility, reliability and validity of the tests we use to measure and investigate it. Vocabulary is a lively and vital area of research and innovation. This volume brings together contributions from internationally-renowned researchers in this field to explain much of the background to study in this area. It introduces to a wider audience the concerns, the new approaches and the most recent developments in the field of vocabulary research and testing.