The legalisation of the customary land rights of rural communities is currently actively promoted as a strategy for conserving biodiversity. There is, however, little empirical information on the conservation outcomes of these tenure reforms. In this paper, we describe four conservation projects that specifically aimed to formalise land rights in the Philippines, a country widely seen as a model for the devolution of control over natural resources to rural communities. We demonstrate that these legalistic interventions are based on flawed assumptions, on: 1) the capacity of the state to enforce tenure; 2) the characteristics of customary land rights; and 3) the causal links between legal entitlements and sustainable natural resource management. As a result, these state-led tenure reforms actually aggravate tenure insecurity on the ground, and ultimately fail to improve natural resource management.