Gayo is a regional language of Indonesia spoken by some 260,000 people in the central highlands of Aceh province, at the north-western tip of Sumatra. The Gayo people have historically had close ties to the majority Acehnese of the coast, while maintaining their distinct cultural and linguistic heritage. Gayo remains the first language of most ethnic Gayo to this day, and it is the vehicle for a rich oral literary tradition. The language belongs to the Malayo-Polynesian branch of the Austronesian family of languages. It is typologically unlike Acehnese, but shares certain features such as voice with the Batak languages of the neighbouring province of North Sumatra. Gayo features a voice system of the type that has been referred to as symmetrical, whereby neither actor nor undergoer voice can be considered the basic or unmarked alignment. The language also features valence-increasing affixes, and a range of verbal affixes that mark intransitive verbs to indicate information about various different semantic types of events. This grammar is the first detailed descriptive account of the phonology, morphology and syntax of Gayo. The analysis draws upon data that reflect the cultural context in which the language is spoken, and in the appendices two Gayo texts with their translations are included.