Good faith has long been recognized in international law. Yet, there is an ongoing debate on its relevance, normativity and scope of application. Thus, this chapter will examine the position that good faith can play in international law. In so doing, it will appraise whether good faith has a normative or rather descriptive character in the ecosystem of international rules, processes and actors. Against this background, this chapter will analyze good faith as a conception governing international law. The analysis will primarily rely on the dogmatic method and the review of basic sources of international law, including treaties and case law. Also, the historic approach will be employed to achieve the purpose of the chapter highlighted above. Through these lenses, the chapter will reveal that good faith is a legal norm and has a non-derogable place in the decentralized international legal order, which bases the creation and performance of international obligations on the will of its subjects. This is a principle governing international law which ensures its coherence and systemic organization, as it both creates and justifies the consistency and effectiveness of international obligations. This contribution will show that good faith creates meaningful relations between various norms of international law. It seems impossible to imagine the efficient existence of international law without good faith. The validity of good faith stems directly from the very essence of international law. This chapter will also show that although good faith is not derived from the will of States, it has a primordial character in relation to that will – it governs it and ensures its fulfillment in accordance with the intentions of parties and the letter and purpose of the obligation(s). While good faith is too general in its nature to impose concrete normative requirements on States, it lays the foundations for other more concrete and specific norms. Therefore, this chapter will identify good faith as a general principle within the meaning of Article 38 (1) (c) of the Statute of the International Court of Justice.