Many services and goods are supplied by non-profit organizations. These social enterprises have a hybrid character, because they possess characteristics of governmental and commercial organizations. Therefore, these social enterprises are also called private-public sector enterprises (PPSEs). Very often PPSEs will qualify as an undertaking within the meaning of the European Union (EU) Treaty, and as a consequence, the EU completion rules will be applicable. On grounds of the non-profit character and/or the activities of the PPSE in the general interest, PPSEs also often benefit from a special tax regime: (partial) exemption or other tax provision. The question arises then whether that regime qualifies as a preferential tax measure that constitutes fiscal State aid. In this analysis, special attention must be paid to the fact that in many cases PPSEs will operate a service of general economic interest, which could justify tax aid. However, in this article, it will be argued that it is very difficult to design tax measure in a way that they are compatible with the strict conditions that the European Court of Justice (ECJ) applies.