This thesis is based on eighteen months fieldwork in the Ese Ejja community of Portachuelo, on the lower Beni River, in northern Bolivia. The Ese Ejja are an indigenous Amazonian people of the Tacana linguistic family. The thesis analyses Ese Ejja ideas of alterity and demonstrates that such ideas are the basis for the construction of identity. Alterity must constantly be created and maintained, however, 'others' pose a constant threat and, therefore, difference must also be eliminated through conviviality and procreation. Drawing on socio-cosmological ideas, myth and everyday life experiences, the argument focuses on the Ese Ejja's ambivalent sentiments towards non-indigenous people, who are considered the epitome of otherness. These sentiments are characterised by both fear and avoidance, and, at the same time, by emulation. Vis-a-vis non-indigenous people, the Ese Ejja display a form of self-deprecation, expressed in the statement that they themselves are not 'the true people'. The thesis analyses the relationship between culturally shared and individually held ideas. Among the Ese Ejja, self-deprecation is the dominant discourse, but ideas vary from person to person and they transform over the course of people's lives. And it is through individual and collective transformations that dominant cultural constructs are refashioned and reproduced. Thus, the thesis stresses the importance of giving voice to the contrasting and contradicting ideas that exist in any social group. It concludes that Ese Ejja identity - constructed through alterity - is better understood as a contingent position rather than an absolute essence. Finally, it is suggested that the notion of not being 'the true people' is rooted in indigenous perceptions of history, viewed as a progressive rapprochement with the non-indigenous peoples.