The present study focuses precisely on the shifting ethnic frontiers and relations over time that have constituted and reconstituted the Piaroa group of the Middle Orinoco region in Venezuela. Whereas much of the new ethnicity literature has been more concerned with the subjective, symbolic and reflexive dimensions of identity politics, the approach that I take looks at broad diachronic trends of boundary movement in relation to changing demographic, economic, political and ecological factors. The dynamic and shifting nature of Piaroa ethnic boundaries and relations was highlighted here through political, ecological and historical analysis. During the past 500 years, the articulation of ethnocultural differences among the Piaroa and their neighbours has passed through three distinct socio-historical phases (pre-contact, post-contact and modern). In the precontact phase, inter-ethnic relationships were characterised as either hostile and territorially segregated, or peaceful, ecologically complementary and economically integrated. The elaboration of ethnic differentiation and structured patterns of inter-ethnic interaction were conditioned by a demographically dense, relatively stable and competitive resource environment. The post-contact phase was marked by peaceful territorial conquest and cultural assimilation of neighbours, following drastic regional population decline and yet increased techno-economic capacitation through ownership of iron tools. Human labour became the strategic resource and, as the focus of competition shifted to people themselves, social and ethnic boundaries faded accordingly. The modern phase can be summed up as increasing intra- and inter-ethnic tensions tied to land and political struggles. Downriver migration, settlement nucleation, population growth and competition over resources provided or sanctioned by the expanding nation state have led to a resurgence of inclusive/exclusive social boundary distinctions at multiple levels. This case study demonstrates that fluctuations in resource relationships that is, the competitive balance among population, resources, land, labour, power and socio-economic ties – are closely tied to the ebb and flow of ethnic categorisation. Although the effective local or regional environment and its impact on ethnicity are often deeply transformed by socio-political forces whose origin may be elsewhere, it can also be seen that local responses to such changes also shape the outcome. In this light, the contemporary ethno-political mobilisation of the Piaroa and their articulation of difference from the national society might well be understood as the unintended consequence of the state’s effort to remake their Indian peoples to look and act more like the dominant criollo population.