The fundamental principles of the OZ provide value-based criteria for conduct in contractual and other obligations relationships. They play an important role in interpreting the legal norms of the OZ and, in exceptional cases, may establish an independent standard of conduct. Certain provisions of the OZ that prove too rigid or harsh in specific real-life situations can be “softened” through appropriate interpretation based on these fundamental principles (e.g., the principle of conscientiousness and fairness). The application of fundamental legal principles is particularly relevant when interpreting and determining the content of specific legal standards, as well as in filling legal gaps.⁴¹ As value-based criteria, they help determine how to fill substantive gaps in legal provisions and which among multiple possible interpretations of a legal rule should be chosen. These principles serve as essential guidance for judges when reconstructing a legal norm that explicitly defines a legal situation along with its legal consequences.⁴² From an economic perspective, these principles act as instruments or mechanisms for preventing and sanctioning immoral behaviour in transactions, which is a direct source of economic inefficiency and reduces overall welfare.⁴³

The fundamental principles of the OZ are:

• The principle of dispositivity (Article 2 OZ)
• The principle of free regulation of obligations relationships (Article 3 OZ)
• The principle of equality (Article 4 OZ)
• The principle of conscientiousness and fairness (Article 5 OZ)
• The principle of diligent conduct (Article 6 OZ)
• The principle of prohibition of abuse of rights (Article 7 OZ)
• The principle of equal value of performances (Article 8 OZ)
• The principle of the duty to fulfil obligations – pacta sunt servanda (Article 9 OZ)
• The principle of prohibition of causing damage (Article 10 OZ)
• The principle of peaceful dispute resolution (Article 11 OZ)

The following sections provide a more detailed presentation of these fundamental principles.