The studies in this book represent the rich, diverse and substantial research being conducted today in the linguistics of Mainland Southeast Asia. The chapters cover a broad scope. Several studies address questions of language relatedness, often challenging conventional assumptions about the status of language contact as an explanatory factor in accounting for linguistic similarities. Several address the question of Mainland Southeast Asia as a linguistic area, exploring new ways to imagine and define the boundaries, and indeed the boundedness, of a Mainland Southeast Asia area. Two contributions rethink the received notion of the 'sesquisyllable' with new empirical and theoretical angles. And a set of chapters explores topics in the morphology and syntax of the region's languages, sometimes challenging orthodox assumptions and claims about what a typical language of Mainland Southeast Asia is like. Written by leading researchers in the field, and with a substantial overview of current knowledge and new directions by the volume editors N. J. Enfield and Bernard Comrie, this book will serve as an authoritative source on where the linguistics of Mainland Southeast Asia is at, and where it is heading.