European Union law is characterized by the existence of a number of closely related manifestations of good faith obligations. Firstly, good faith has been applied by the European Courts in the manner familiar from public international law. Secondly, the duty of sincere cooperation in Article 4(3) Treaty on European Union is the source of a variety of rules of cooperation, compliance and conflict resolution. Finally, a principle of solidarity exists in EU law that has been applied to appeal to ideas of fairness between the Member States of the Union.