This book summarizes the results a three-year longitudinal project on Mandarin development among children of Indonesian mothers, the second largest non-Mandarin speaking immigrant group in Taiwan. These children were acquiring their first language while interacting primarily with a non-native learner of the language. The book discusses phonological, lexical and syntactic development to provide a better understanding of the language development of the children of immigrants and has important implications for language education policy and language acquisition theories.