While conservation activities are underfunded almost everywhere, the gap between current expenditure and what is needed is particularly extreme in the tropics where threatened species and habitats are most concentrated. We examine how to bridge this funding gap. Firstly, we try to identify who in principle should pay, by comparing the spatial distribution of the costs and the benefits of tropical conservation. The immediate opportunity costs of conservation often exceed its more obvious, management-related costs, and are borne largely by local communities. Conversely, we argue that the greatest benefits of conservation derive from ecological services, and from option, existence, and bequest values; these are often widely dispersed and enjoyed in large part by wealthier national and global beneficiaries. We conclude that the gap in funding tropical conservation should be borne largely by national and especially global communities, who receive most benefit but currently pay least cost. In the second part of the paper we review recent developments in order to examine how in practice increased funding may be raised. There are many growing and novel sources of support: private philanthropy, premium pricing for biodiversity-related goods via certification schemes, and the development of entirely new markets for environmental services. Despite their potential, we conclude that the principal route for meeting the unmet costs of tropical conservation will have to be via governments, and will inevitably require the transfer of substantial resources from north to south. This will be enormously difficult, both politically and logistically, but without it we believe that much of what remains of tropical nature will be lost.