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. This volume serves to generate new directions and advances in bilingualism research.