The classification of PPP contracts for the application of the Directive 2004/18/EC is not an easy task. This is due to the fact that PPP contracts usually include several types of different activities, such as public works, supply, service, or even establishment of an institutional framework for PPP. For the classification of contracts which include works, supplies and services, the Directive establishes a form of mixed contracts, on the basis of which appropriate provisions are able to be applied. However, the question remains whether the same form of mixed contracts may be used for PPPs, including the establishment of IPPPs and, if so, how the rules should be interpreted. Using the CJEU’s rulings in Loutraki C-145/08 and Oulun Kapunki C-215/09 the author will show that applying the theory of mixed contracts to the classification of IPPPs poses certain legal uncertainties. These legal uncertainties may include the scope and extent of the indivisibility of the contract (which is a requirement of an existence of the mixed contract), as well as bases for separation of the certain elements of the contract. The author will analyse both cases and will pay particular attention to the details which may lead to different CJEU’s decisions.