This volume presents a series of studies and reviews that provide insights into grammatical variation and the development of code-switching in neurotypical speakers, as well as into language mixing practices among individuals with neurodevelopmental conditions. Across seven chapters, a range of themes is explored, including: community norms and language practices, the influence of caregivers on bilingual development, attitudes and ideologies surrounding bilingualism, code-switching as a communicative resource, and the intersection of neurodiversity and bilingualism. By offering up-to-date perspectives on these topics, the volume builds on existing research into code-switching, such as work by Margaret Deuchar, and it highlights open data initiatives for advancing future research in this area.