Ever more governments around the world are defining and implementing “open data” strategies in order to increase transparency, participation and/or government efficiency.

The commonly accepted premise underlying these strategies is that the publishing of government data in a reusable format can strengthen citizen engagement and yield new innovative businesses. However, as these open data strategies are relatively new, evidence of this expected impact is still limited. Important questions currently debated are: What is an appropriate open data strategy for governments? Why are some governments succeeding in opening up their databases and others struggling? How can open data policies contribute to increase citizens’ trust and participation in government and provide an economic spur? In an inquiry for the Dutch Ministry of the Interior and Kingdom Relations, TNO (the Netherlands Organisation for Applied Scientific Research) examined the open data strategies in five countries and gathered anecdotal evidence of its key features, barriers and drivers for progress and effects. In this article we will give a brief overview of the research results and define key challenges for effective open data policy. Two of the main conclusions are that sound evidence of the precise effects is lacking (e.g. economic, social and democratic effects) and that the acquisition of more knowledge could strengthen a well-informed debate, remove governments’ reluctance to invest in open data strategies and help them to develop an effective policy.