International commercial arbitration is an efficient, fast, and amicable way of resolving any disputes which arise between two commercial parties. At the heart of the arbitral proceeding is the arbitration agreement. Like everything in the law domain, an arbitration agreement must be governed by some law or rules. This requirement is especially important in case any question of validity or existence arises. That is why parties’ autonomy exists, so the parties can choose any system of law that fits their arbitration agreement. If the parties don’t make an express choice of law, the arbitral tribunal has to decide on the governing law based on some established principles. These established principles are choice-of-law rules that are widely used in juridical practice and talked about among legal scholars. Consequently, by using these choice-of-law rules the arbitration agreement can be governed by at least four possible governing laws. These are the law expressly chosen by the parties, the law impliedly chosen, the law of the seat, and the law of the underlying contract. When determining the appropriate law, the separability presumption has to be kept in mind. The separability presumption ensures that an international arbitration agreement is presumptively separable from the underlying contract with which it is associated. Also, when talking about the governing law, it is important to mention the validation principle. According to the validation principle, when parties chose two laws (ex. the law of the seat and the law of the underlying contract) the law which gives effect to the arbitration agreement will apply. Hence, its mission is to save the arbitration agreement from possible invalidity.