In the Maluku Islands of Eastern Indonesia, a center of global diversity in coral reef systems and the historic center of trade in cloves and other spices, tenure practices known as sasi have flourished for at least a century. This article analyzes changes in the ways Dutch colonial officials, Indonesian government officials, and environmental NGOs have interpreted Moluccan customary law and local institutions. Dutch colonial accounts of sasi, a generic name for a historic family of institutions, laws, and ritual practices that regulated access to fields, reefs, and rivers, suggest that sasi was a synthetic, highly variable body of practices linked to religious beliefs and local cultural ideas of nature. During the past two decades, as international and national conservation discourses have proliferated and a movement has developed to support indigenous Indonesian cultural communities, Indonesian NGOs and the Ministry of the Environment have promoted, and largely created, images of sasi as an environmental institution and body of customary law promoting sustainable development, conservation, and social equity. This article focuses on how sasi has been continuously reinterpreted by a variety of actors, following the trajectory of changing institutional interests and images.