In the world today, bilingualism is more common than monolingualism. Thus, the default mental lexicon may in fact be the bilingual lexicon. More than ever, social and technological innovation have created a situation in which lexical knowledge may change dramatically throughout an individual’s lifetime. This book offers a new perspective for the understanding of these phenomena and their consequences for the representation of words in the mind and brain. Contributing authors are leaders in the field who provide a re-analysis of key assumptions and a re-focusing of research. They bring new insights and new findings that advance the understanding of both bilingualism and the mental lexicon.