This volume comprises 16 chapters – both research papers and theoretical contributions – grouped in three thematic sections. The chapters in the first part, entitled Discourse Communities: Languages in Contact, adopt a social and/or historical perspective on bi-/multilingualism. The contributions in the second part, entitled Languages in the Mind: Language Development and Language Use, view issues related to bi- and multilingualism from psycholinguistic and psychological perspectives. The chapters comprising the third part, Language Education: Supporting Multilingual Development, adopt a broadly understood didactic perspective on bi-/multilingualism.