Cook Islands Māori is an endangered East Polynesian language closely related to but distinct from Tahitian and New Zealand Māori. This project focusses specifically on the varieties of Cook Islands Māori originating from, and spoken in, the Southern Group of the Cook Islands, that is, the islands of Rarotonga, Aitutaki, Atiu, Maꞌuke , Mitiꞌaro and Mangaia. These varieties are collectively known as Southern Cook Islands Māori or Te Reo Māori o te Pae Tonga o te Kuki Airani. This thesis is a grammatical description, following the principles of ‘basic linguistic theoryʻ or the ‘theory neutral’ position of contemporary descriptive linguistic scholarship (Dryer, 2006; Dixon, 1997), of Southern Cook Islands Māori. The areas of the grammar that are covered are: the phonetics, phonology, morphology and syntax of simple and complex sentences. Over the course of this project over 60 hours of audio-video material was archived as part of the ongoing documentation of this language.