In this paper, I explore the question of how the costs of undertaking an important type of climate change mitigation should be shared amongst states seeking an environmentally effective and equitable response to global climate change. While much of the normative literature on climate mitigation has focused on burden sharing within the context of reductions in emissions of greenhouse gas, I explore the question of how the costs of protecting tropical forests in order to harness their climate mitigation potential should (...) be distributed amongst developing and developed states. In response to this question, I outline and defend a ‘beneficiary pays’ account of forestry mitigation burden sharing that requires affluent states to finance measures supporting avoided deforestation while less affluent states, within whose territory these forests tend to be located, implement these measures. The normative basis for this account, I argue, is a principle of ‘unjust enrichment’ according to which developed states must bear much of the cost of avoided deforestation for its climate mitigation potential because of the huge economic benefits their citizens have accumulated from productive activities that have contributed to climate change. (shrink)