This volume explores the implications of cross-linguistic structures in simultaneous bilingualism. It aims to find cognitive explanations for the presence or absence of cross-linguistic structures that go beyond the debate of 'one system or two'. The contributors present syntactic, morphological and phonological features that are found in bilingual children, but are untypical of monolingual development, and discuss pertinent methodological issues. The orientation of this volume stands out from competing volumes in the field in that the focus is not limited to similarities between monolingual and bilingual first language acquisition. The volume will be of interest to researchers in the field of bilingualism and primary language acquisition, language theorists, and professionals working with bilingual populations.