Semelai is a previously undescribed and endangered Aslian (Mon-Khmer) language of the Malay Peninsula. This book - the first in-depth description of an Aslian language - provides a comprehensive reference grammar of Semelai. Semelai intertwines two types of morphological system: a concatenative system of prefixes, suffixes and a circumfix - acquired through extended contact with Malay - and a nonconcatenative system of prefixes and infixes (including infix reduplication), inherited from Mon-Khmer. There are distinctive word classes - Nominals, Verbs and Expressives - the latter iconic utterances which simultaneously provide information about the predicate and its arguments. Semelai has many derivational processes which change word class or affect transitivity, and it combines both head-marking and dependent-marking profiles. It also has a rich phonemic system of 20 vowels and 32 consonants. Nicole Kruspe's discussion is complemented with a generous number of illustrative examples and texts, creating a reference work that will be welcomed by descriptivists and typologists alike.