The purpose of this article is to report on the initial development of a theoretically grounded and empirically validated scale to measure global citizenship. The methodology employed is multi-faceted, including two expert face validity trials, extensive exploratory and confirmatory factor analyses with multiple datasets, and a series of three small-group interviews utilizing nominal group technique to verify the scope of the global citizenship construct. The findings provide support for a three-dimensional Global Citizenship Scale that encompasses social responsibility, global competence, and global civic engagement. Global competence and global civic engagement are both strong dimensions of global citizenship, and each has three reliable subdimensions that add further refinement to the construct. Social responsibility proves to be a dimension of global citizenship with a less clearly defined structure. The Global Citizenship Scale and its conceptual framework have important implications for education abroad outcomes research and practice. (Contains 2 figures and 6 tables.)