Scholars' criticism of transparency in public-private partnerships (PPPs) often focuses on 'external' transparency, that is, the extent to which internal information is visible to the outside world. However, to achieve external transparency, internal transparency - the availability and inferability of information for the public procurer and the private party - is crucial. In this article we analyse input, process, and output transparency from three different perspectives (institutional, cognitive, and strategic) in four PPPs in the Netherlands. We conclude that input transparency is high, but process and output transparency less so. Moreover, output transparency has gained importance in PPPs. Whether this is problematic depends on the PPPs' institutional environment. In some partnerships the desired output is uncontested and predetermined by clear standards in the institutional environment, whereas other PPPs deal with contested output norms, decreasing the partnerships' transparency. These results nuance the current debate on the lack of transparency in PPPs.