Bilingualism and the study of speech sounds are two of the largest areas of inquiry in linguistics. This Handbook sits at the intersection of these fields, providing a comprehensive overview of the most recent, cutting-edge work on the sound systems of adult and child bilinguals. Bringing together contributions from an international team of world-leading experts, it covers all aspects of the speech perception, production and processing of bilingual individuals, as well as surveying cross-linguistic influences on the phonetics and phonology of bilingualism. The thirty-five chapters are divided into thematic areas covering the theoretical foundations and methodological approaches employed to investigate bilingual speech, overviews of major findings and developments in child and adult bilingual phonology and phonetics, descriptions of the major areas of research within the speech perception, production and processing of the bilingual individual, and examinations of various predictors of cross-linguistic influence and variables affecting the outcomes of bilingual speech.