ISO 26000 is a new international standard on social responsibility developed by the International Organization for Standardization (ISO). It offers guidance across themes including human rights, labour, environment, consumer protection, fair operating practices and community development. The brand recognition of ISO standards, ISO's geographical scope and its credibility among market actors mean that ISO 26000 has the potential to improve the practice of social responsibility in local and global markets. The reach and scale of ISO 26000's impacts has important implications for governance and public policy.~~Standards - and market governance mechanisms more broadly - should be analysed not only in terms of their direct impact on environmental, social and economic factors but also in terms of their interaction with policymaking and global governance. ~~The evolving relationship between market governance mechanisms and public governance, both national and global, has not been adequately considered to date. But this relationship matters for sustainable development. ~~This paper describes the development of the ISO 26000 standard and discusses the dissonances that emerged in relation to policymaking, global governance and consequently sustainable development. The paper suggests a number of steps that could be taken to maximise the positive contributions of ISO 26000 to global governance for sustainable development and offers lessons for the analysis of other market governance mechanisms.