Abstract
The new Public Procurement Law establishes that contracting authorities and contractors are obliged to cooperate concerning the performance of procurement contracts to ensure that they are executed properly (Article 431). The essence of the obligation to cooperate includes loyal behaviour towards the contractor, understood as respecting its interests. As a result, the content of the obligation is extended by certain additional obligations that are not stipulated directly by the contract or the law. However, what makes up this bundle of additional obligations is case specific, i.e. it depends on the specific factual conditions of a certain case. Respectively, it may be a matter of both refraining from actions that prevent or hinder the performance of a contract and taking actions that facilitate it. This is not a new solution in Polish law, as the principle of cooperation between the parties concerning the performance of a contract has long been provided for in the Civil Code. Therefore, for Article 431 of the PPL not to be considered superfluous, it seems justified to suggest introducing further amendments in the law as a result of which the obligation to cooperate should apply to all participants in the public procurement proceedings from the moment the proceedings are initiated.