Book excerpt: This book presents the latest developments in crosslinguistic influence (CLI) and multilingualism research. The contributors, both veteran researchers and relative newcomers to the field, situate their research in current debates in terms of theory and data analysis and they present it in an accessible way. The chapters investigate how and when native and non-native language knowledge is used in language production. They focus on lexis, syntax, tense-aspect, phonology of multilingual production and link it to a range of concepts such as redundancy, affordances, metalinguistic awareness and L2 status. The empirical data have been collected from participants with a wide combination of languages: besides English, German, French and Spanish, there is Finnish, Swedish, Polish, Chinese and Catalan.