Markets for ecosystem services are being promoted across the developing world, amidst claims that the provision of economic incentives is vital to bring about resource conservation. This article argues that equity and legitimacy are also critical dimensions in the design and implementation of such markets, if social development goals beyond economic gains are to be achieved. The article examines this issue by focusing on two communities involved in a project for carbon sequestration services of forests in the state of Chiapas, Mexico. The perceived legitimacy of the activities and the distribution of economic outcomes and project-related information are found to be mediated by organizational allegiances and the history of social relations regarding access to property and forest resources. Political affiliation determines the project's legitimacy, while the poorest farmers and women have been excluded from project design and implementation. The authors argue that pitfalls such as these contribute to reinforcing existing power structures, inequities and vulnerabilities, and suggest that this is a product of the nature of emerging markets. Markets for ecosystem services are, in effect, limited in promoting more legitimate forms of decision making and a more equitable distribution of their outcomes.