 There is a growing recognition that insufficient attention has been paid to the outcomes measured in clinical trials. These issues could be addressed through the development and use of an agreed standardized collection of outcomes. Key issues to consider in the development of a core outcome set include its scope, the stakeholder groups to involve, the choice of consensus method and the achievement of a consensus. This article was authored by Williamson Paula R., Altman Douglas G., Blaise B. Jane M., and others.