This review draws on literature from Reversing Language Shift (RLS), Second Language Acquisition (SLA) and Māori and indigenous language education to identify help/hinder factors for second language (L2) proficiency development in te reo (the Māori language). Ten factors each with the potential to help or hinder the development of second language Māori proficiency amongst adult learners are identified, and an adult Māori language proficiency research agenda is proposed. The purpose of the research agenda being: to explore the relative importance of the 10 factors for adult learners seeking to develop proficiency in te reo.