‘Much as monolingualism represents an idealized fiction, so does multilingualism when it is understood as complete heterogeneity or chaos. The reality is somewhere in between.’ (243). Siemund's book offers a critique of the relationship between monolingualism and multilingualism in the globalising world. This relationship is explicated through an analysis of multilingual development processes, focusing on the development of English in multilingual urban societies. The analysis maps a constellation of factors influencing the outcomes of interactions between heritage languages, national languages, and global English in specific multilingual ecologies.

Set against the background of rapid globalisation and changing forms of multilingualism in history (chapter 1), the book is guided by a rigorous review of multilingual research across linguistics, psychology, and education studies produced over the past century (chapters 2–5). This review points to two theoretical themes: the potential advantages of multilingual development (chapters 2 and 4) and the factors influencing the direction of cross-linguistic influence in multilingual development (chapters 3 and 5). The reader is pointed in particular to the impacts of multilingual development on metalinguistic awareness and the production of language dominance as linguistic factors (e.g. proficiency, exposure, and use) that interact with extra-linguistic factors (e.g. language ideologies and policies) in multilingual individuals and societies.

Theoretical insights derived from the review are used to inform three case studies on the development of New Englishes in Singapore, Hong Kong, and the Gulf Region as distinct multilingual ecologies with differing immigration patterns (chapter 6). Each case study is structured as a three-part analysis. It begins with a historical analysis mapping the trajectories of immigration and the assemblage of languages thus formed (historical multilingualism). This is followed by a societal analysis of the current forms of multilingualism produced by the interaction between official language policies and other normative language beliefs in society (societal multilingualism). Each case ends with an analysis of the linguistic and social factors giving rise to the local varieties of English. The case studies highlight how different immigration patterns formulate distinct multilingual ecologies from which diverging varieties of English emerges. The Gulf Region offers a novel case in which English emerges as a lingua franca not simply in contact with other languages but with different varieties of Englishes brought in by immigrants under economic globalisation (226), forming ‘a highly pragmatically organized code’ (223).

The extensive literature review and the case studies are integrated to produce four main theoretical contributions (chapter 7):

• • a conceptual map of the linguistic and extra-linguistic factors influencing multilingual development (229, 231)

• • a critical reflection on the ‘political and normative’ (233) dimensions in the evaluation of multilingual advantages

• • a reconceptualisation of monolingualism and multilingualism as different forms of social organisation functioning on a spectrum between homogeneity and heterogeneity (241)

• • a new typology of English drawn with a focus on immigration groups and the local multilingual ecologies thus formed (251)

This book offers theoretical and empirical insights into the future directions for studying multilingual development. Its rich interdisciplinary literature review also makes it a helpful resource book for students who are new to the topic.