The new operational environment generated by the mass media revolution and the advent of the global information society lays the ground for a generalized re-emergence of public diplomacy (PD). After having been dismantled during the 1990s, this branch of foreign policy is undergoing a redevelopment phase within the chancelleries of many states around the globe. The growing salience of public opinion and the exponential development of the new information and communication technologies predispose this diplomacy of persuasion to play an increasing role at the forefront of twenty-first century international relations.Inspite of the increased importance that public diplomacy is acquiring, the question of its real effectiveness nevertheless remains unanswered. For the moment, governments are still unable to determine to what extent their PD initiatives are able to influence foreign audiences or contribute to the achievement of their foreign policy goals. Without a valid evaluation tool, PD will remain condemned to play a secondary role within states' foreign policy systems. This article addresses the main aspects of this issue by analysing the many technical and methodological problems that are attached to PD evaluation, exploring research avenues that could remedy these gaps, and thus helping to resolve a problem that is still underestimated yet bound to become increasingly important in the 'hyper-media' age of international relations.