Phonemic awareness and phonetic skill are the backbones of phonological theory. In phonological acquisition, the presence or lack of the former crucially determines the outcome of the latter. This inescapably becomes a common thread that interweaves developmental phonology in both childhood and adulthood. Child and adult-learner speech in the course of development constitute separate linguistic systems in their own right: they are intermediate states whose endpoint is, or ought to be, mastery of targeted speech either in a first or a second language. These intermediate states form the theme of this volume which introduces the term protolanguage (to refer to child language in development) and juxtaposes it with interlanguage (to refer to language development in adulthood). Although major languages like English and Spanish are included, there is an emphasis in the book on under-reported languages: monolingual Hungarian and Swedish and bilingual combinations, like Greek-English and German-English. There is also a focus on under-represented studies in IL: L2 German from L1 French; L2 English from Catalan and Portuguese; and in dialectal acquisition of Ecuadorian Spanish from Andalusian speakers. This volume brings together different methodological approaches with a stress on both phonetic and phonological analysis. It includes both child and adult developmental perspectives, descriptive and/or theoretical results from a combination of methodological approaches (e.g. single-case, cross-sectional; spontaneous speech samples, narrative retells) and a consideration of speech acquisition in the general context of language. The volume aims to motivate a shift in the general tendency among researchers to specialize in language subfields (L1 acquisition; L2 acquisition, bilingualism; typical/atypical language) of what is actually one common linguistic domain, i.e. the study of speech sounds (phonology/phonetics).