Developments in research have practical relevance for guiding early language intervention and thereby reducing the risk of poor language development in children with communication disorders. Given the variability involved in the acquisition of disparate languages in monolingual, bilingual and bi-dialectal settings, linguists deciphering the process of language acquisition are faced with the task of designing and coordinating studies where such acquisition can be legitimately compared. This has immediate repercussions for the work of clinical linguists and language pathologists, where a common challenge crosslinguistically is to validate the efficacy of assessment and screening tools that identify and differentiate disordered from normal linguistic behaviour in children. Owing to a lack of assessment materials in many languages, batteries standardized for use in one language (or dialect) are often utilized to assess another, and batteries designed for a monolingual population are utilized to assess language in bilingualism.

There are numerous books on child language acquisition, monolingual and bilingual, presenting clear and concise introductions to main concepts, issues and debates (e.g. Bhatia & Ritchie, 2012; Clark, 2009; Grosjean, 2010; Lust, 2006). Some recent titles address specific language impairment and communication disorders in children in general (e.g. Leonard, 2014) and in multilingual contexts (e.g. Armon-Lotem et al., 2015; Patterson & Rodriguez, 2016). McLeod and Goldstein (2012) explored both multilingual and multicultural aspects of children with speech sound disorders. The focus in some of the existing books is on a specific major language, like Spanish (e.g. Grinstead, 2009) or on a specific language level, like phonology (e.g. Hua & Dodd, 2006) or morphology (e.g. Grohmann & Neokleous, 2014).

The present volume brings together a number of studies on typical and atypical language acquisition, purposefully turning diversity into a core theme. Diversity is underscored here in terms of linguistic typology, types of language acquisition, the language level examined, the language context, research methodologies and proposed assessment tools.