This thesis explores how people’s knowledge about sustainability affects participation in combined conservation and development initiatives. It focuses principally on two case studies that embody these dual objectives: the ‘conservancy programme’ in Namibia and the Alto Bermejo Project in Argentina. The concept of sustainability – of living in a way that meets both current and future needs – has led, on a global scale, to a re-casting of the relationship between conservation and development as one of necessary interdependence. Such is the credibility invested in the concept of sustainability that it is found underpinning policy and intervention in countries as distinct as Namibia and Argentina. These observations set up the two central questions of the thesis. First, what types of participation characterise decision-making processes within these two contexts? Second, how is having knowledge on sustainability one (though not the only) causal determinant of who participates, in what activities and on what basis? These questions pave the way for analysis of the types of participation found in two Namibian conservancies and specific components of the Alto Bermejo Project in Argentina. A key belief shaping policy and intervention in both contexts is that wider local involvement is a precondition of sustainable natural resource use. Consequently, strong efforts are made in both places to attempt to ensure that local people are key decision-makers. However, talk of local-level, grassroots participation in the Namibian or Argentine context, whilst by no means wholly misplaced, can obscure the high participation levels of NGO, government and specific private-sector actors. This is because both initiatives depend for the achievement of their objectives on a process of knowledge transfer from implementers to beneficiaries. Much of the knowledge deemed necessary for the realisation of these objectives lies with government, NGO and specific private sector actors. Having this knowledge, therefore, renders their participation indispensable. Indeed, the very access of these actors to the resources on which intervention depends is partly a function of the credibility invested in their knowledge. Access to resources is also a means through which the credibility of such knowledge is reinforced. This dynamic I call ‘circularity in intervention’. ‘Circularity in intervention’ entails a variety of advantages and disadvantages relative to context and perspective, which this thesis neither condemns nor condones. It does, nonetheless, seek to clarify one important point. Our account of participation in the Namibian or Argentine examples is incomplete without looking at how having or not having knowledge about sustainability affects participation.