International development organizations increasingly use advocacy as a strategy to pursue effectiveness. However, establishing the effectiveness of advocacy is problematic and dependent on the interpretations of the stakeholders involved, as well as the interactions between them. This article challenges the idea of objective and rational evaluation, showing that advocacy evaluation is an inherently political process in which space for interactions around methods, processes and results defines how effectiveness is interpreted, measured and presented. In addition, this article demonstrates how this space for interaction contributes to the quality and accuracy of evaluating advocacy effectiveness by providing room to explore and address the multiplicities of meaning around identifying, measuring and presenting outcomes.