This chapter examines the concept of good faith within the Polish legal system, focusing on its interpretation in legislation, case law, and academic literature. It traces the development of good faith as a legal principle, outlining its sources of inspiration, legal basis, and constitutional practices. Although the Polish Constitution does not explicitly mention or define good faith, the Constitutional Tribunal upholds it as a fundamental principle, assuming its existence as inherent to a democratic state governed by the rule of law (Article 2 of the Constitution). The Constitutional Tribunal anchors this principle in the idea of citizens’ trust in the State and its laws, while the Supreme Court associates it with the protection of good customs and principles of social coexistence. The analysis demonstrates that the commitment to protecting good faith is reflected across various fields of law, influencing both legislative development and enforcement practices. While some scholars argue for a coherent interpretation of good faith across legal contexts, such unification appears impractical. Nevertheless, there is a consensus that good faith remains essential to promote trust, legal certainty, and predictability, requiring respect for the rights of third parties and the legitimate interests of individuals in legal transactions.