Certification systems are becoming important tools to encourage and reward social and environmental responsibility. This paper explores whether these systems, which generally have not been designed for the explicit aim of poverty reduction, can assist poor people, either individually or in community-based and small-to-medium production units, to build their natural assets as a basis for sustainable livelihoods. The paper examines two leading certification systems -- the Forest Stewardship Council(TM); and the Fair Trade Certified(TM); system -- and emerging systems in tourism and mining. The results to date have been mixed. In the forestry sector, poverty reduction benefits of certification have been modest relative to its environmental benefits. In the agricultural commodity trade, where certification systems have been designed with a stronger focus on reducing poverty, the benefits have been greater. The long-term challenge is to ensure that the rapid global uptake and 'mainstreaming' of certification systems does not create new hurdles for low-income individuals and communities.