This paper is an exploration of the relationship between a conservation intervention and the quest for local institutional legitimacy and conservation success through co-management. More precisely, this paper will employ the case of Xcalak Reefs National Park (PNAX) to illuminate the interaction between contextual and procedural elements of co-management implementation, how these variables affect the production of legitimacy in the minds of local resource users, and how resultant attitudes can subvert both management devolution and resource conservation. The failure to produce co-management will be related to the mismatch inherent in attempts to map co-management onto a histories and institutions that do not align with the morality and practicalities necessary for its implementation. In conclusion, the author points out that the Xcalak story shows the way in which varied perspectives on the reason, rationale, and constituency of conservation affect the process and outcomes. PNAX brings to the forefront the inherent conflicts between the desires and expectations of communities, NGOs, and the federal government. Local actors want to conserve resources to maintain their utilization and control. The other actors’ interest lies in serving the national and global constituency’s need for the conservation of the global biodiversity “commons.” The PNAX case shows how these contradictions play out in management, as well as the effects upon community opinion and use of resources. Ultimately, PNAX and Xcalak demonstrate that, regardless of which commons we are trying to promote (local or global), much more attention needs to be paid to contextual variables, the process of project implementation, and their influence on local opinion and behavior. If not, the aims of conservation and community development will remain elusive at best.