This thesis explores how Katuic-speaking indigenous groups in the Central Annamitic Cordillera of Vietnam and Laos understand their environment – hills, streams and forest. Katuic eco-cosmology assumes that the natural landscape is imbued with spirit agents, with whom people must continuously communicate lest misfortune will strike and their livelihoods fail. The thesis posits the hypothesis that these spirit beliefs, and a variety of taboo notions accompanying them, can be interpreted as expressions of a complex socio-environmental adaptation. Today, the indigenous groups in the study region are confronted with a massive development- and modernisation push on two fronts – that of the global development industry on the one hand, and the implementation of national development policies and programs as part of the high-modernist state project in communist Vietnam and Laos, on the other. A second objective of the thesis, then, is to examine the effects of this multi-layered and multi-scaled confrontation on indigenous cosmology, livelihood and landscape. It is argued, this confrontation at the development frontier can be conceived of as an interface between different ontologies or reality posits – one animist, articulated in a relational stance towards the landscape; the other, a naturalist or rationalist ontology, expressed as an objectivist stance towards nature and embodied in the high-modernist development schemes and programs unfolding in the region with the aim of re-engineering its indigenous societies and exploiting its natural resources.      Large parts of the Central Annamites were severely impacted by the Vietnam War; uncounted numbers of minority people were killed, or had their villages destroyed or relocated while defoliants, bombs, and forest fires ravaged the landscape. In the decades that followed the war, the entire social and natural landscape has been reshaped by national development policies and the modernist visions that underpin them. The thesis attempts to understand this physical and cultural transformation of the landscape, focusing particularly on the gradual breakdown of the complex indigenous socio-religious institutions that appear to have played an important functional role in maintaining the pre-war structure of the landscape. The thesis is based primarily on fieldwork carried out between 2004 and 2009 in the provinces of Quảng Nam and Thừa Thiên–Huế in Vietnam and Sekong in Laos.