This paper describes some of the challenges of meeting standards for multiple benefit forest carbon and other land use based carbon projects. There is considerable current controversy about the social and equity impacts of such projects. The authors argue that a combination of more robust standards, such as the Climate Community and Biodiversity (CCB) Standards, for assessing the social performance of projects, and cost-effective impact assessment methods can do much to ensure positive outcomes for local people or communities, and greatly reduce the risk of negative ones. The paper is structured around the following main themes: what is meant by social impact assessment (SIA); a discussion of the requirements of the CCB Standards as regards SIA; key challenges to measuring the social impacts of land use based carbon projects; presentation of seven proposed SIA stages contained in a Manual for SIA released by four prominent non-governmental organisations; and some ‘good practice’ principles for cost-effective SIA.