This article presents a review of medium-of-instruction policy in Timor-Leste after ten years of independence. The review is set against the provisions for language in the country's National Constitution and the human development discourses of the Education for All (EFA) and Millennium Development Goals (MDGs). It is informed by a range of literature dealing with language policy and the medium of instruction in linguistically diverse and developing contexts. The article provides an overview of the language situation and the development challenges facing education planners, followed by a critical examination of medium-of-instruction policy over the period 2000-2012. This critique is followed by an explanatory discussion of the mother tongue-based multilingual education (MTB-MLE) policy for Timor-Leste and a consideration of some concerns about MTB-MLE. The article closes with an assessment of the potential of this policy to promote linguistic diversity in Timor-Leste and help deliver on the EFA and MDGs for 2015. Keywords: Timor-Leste; Education for All; Millennium Development Goals; language in education; medium-of-instruction policy; linguistic diversity; mother tongue-based multilingual education.