International standards and rules increasingly apply to public procurement. Overlapping sets of norms, however, may generate complex relationships between existing disciplines and, even, conflicts of law. On the one hand, international organizations apply several common procurement standards. The WTO Government Procurement Agreement (GPA), the World Bank Procurement Guidelines and several conventions and bilateral free trade agreements set forth a number of basic principles, such as transparency, fairness and participation. On the other hand, however, each organization and procurement standard-setting body elaborates its own, peculiar procedural norms. The main example consists in non-discrimination mechanisms, in rules regarding access to competitions, qualification conditions and award criteria. The existence of a number of procurement standard-setting bodies raises the following main issues: what are the implications of the differences among relevant substantive and procedural models? How to address and solve potential conflicts between incompatible international public procurement standards and the underlying one between the different organizations and financial institutions? The Author finds that sometimes the rules deriving from different internationalizing sources are congruent and compatible (or even identical). For the most part, conflicts or incongruities between international procurement rules are caused by an absence of mechanisms for adapting or reconciling the specific methods used by different supranational bodies’ to protect their interests. The conflict is caused in applying identical principles and is not, therefore, irresolvable. As a result, in the cases considered, a reconciliation of those conflicts of rule cannot disregard an all-inclusive consideration of the significant principles, common to the various regimes.