The feature that most attracts private parties from different states to referring their dispute to an arbitral tribunal is the flexibility of the procedure. However, the differences between arbitration and court litigation are not only procedural, but they concern the substance of the parties’ cases. This is because in the realm of international arbitration the law applicable to the merits of the case is determined according to other provisions than the statutory conflict of laws rules. Depending on the arbitration law of the seat, the entire private international law statute can be captured in a single provision – “absent the parties’ choice, the arbitral tribunal shall apply the rules of law which it determines to be appropriate”. It follows that arbitral tribunals, unlike state courts, are not bound by the conflict of laws rules of the forum. What’s more, the merits of a dispute submitted to arbitration may be governed not only by some national body of law (e.g. the Polish Civil Code) but also by a non-state, nonnational set of provisions – “rules of law” (e.g. the UNIDROIT Principles of International Commercial Contracts). The aim of this article is to analyze how the parties and tribunals may make use of their autonomy in determining the law applicable to a dispute. Furthermore it examines whether there are any limits thereto in light of the Rome I Regulation.