Wh-in-situ is one of the central issues to the research of syntax in natural languages. However, related phenomena in South East Asian languages are still poorly understood. From a formal syntactic perspective, this monograph examines closely various wh-constructions in Vietnamese through island conditions, intervention effects and indefinite wh-construal, and proposes an unselective binding analysis that is different from a recent study. In addition to language-internal phenomena, this book also addresses the crosslinguistic typology of wh-in-situ by comparing a number of unrelated languages within the Minimalist Program approach. It is hoped that the current study can contribute to our understanding of the syntactic structure of Vietnamese specifically, and to the research agenda of wh-in-situ more generally.