The first principle embodied in Article 6 is the principle of party autonomy: the parties are free to choose the law applicable to their contract. Most legal systems recognise this principle. The second principle is the non-mandatory character of the CISG. All provisions are non-mandatory; the only exception is Article 12 CISG.

(a) Such a choice is somewhat ambiguous and can be interpreted in different ways. One could argue that it amounts to an implied exclusion of the CISG, because otherwise the choice would have no practical meaning (cf C 6-1). One could, however, also argue that the choice of the law of a Contracting State identifies the national law to be used for filling gaps in the Convention and avoids the detour through private international law.

(b) In C 6-1, the majority of the Arbitral Tribunal adopted the view that the parties excluded the CISG by agreeing on Italian law. However, there was a dissenting opinion by one of the arbitrators. He took the position that was later also adopted in C 6-2, C 6-3, namely that the choice of the law of a Contracting State does not amount to a opting-out of the CISG. (see the German Supreme Court joined this view in its decision of 11 May 2010, CISG-online 2125.) This latter approach is preferable: the Convention, when adopted, becomes part of the law of the Contracting State. When the parties choose this State’s law, the choice includes the Convention as the law governing international sales contracts, and matters not governed by the Convention are governed by the domestic law of that Contracting State. In other words, the choice of the law of a Contracting State is a derogation from Article 7(2) CISG in that the law applicable to matters not governed by the CISG will not be determined by the conflict of laws rules of the forum. Rather, by choosing the law of a Contracting State, the parties agree on the law which applies to CISG-external gaps.

(c) The CISG Advisory Council has adopted the view that the mere choice of the law of a Contracting State does not exclude the application of the CISG.

(d) The effectiveness of an opting-out clause is subject to the CISG and depends first and foremost on an unambiguous wording. Two examples are:

‘The parties submit the present contract to the domestic law (or: “the Commercial and Civil Code”) of State X.’

‘The CISG does not apply to the present contract.’

It depends on the applicable private international law rules and the degree of party autonomy they grant.

(a) In both cases, the question is governed by the private international law of the forum. In the first case, the parties’ choice of law must comply with the formal and substantive requirements of the applicable private international law. In the second case, the law applicable to the contract will be determined objectively, for which most conflict of laws rely on the criterion of ‘closest connection’.

(b) The question is governed by the CISG, Article 11, Articles 14 et seq., Article 29.

(a) It is extraordinary because those principles are, by definition, non-mandatory soft law. Thus, any mandatory character of a provision of the PICC must be understood as mere indication of the importance of that provision rather than as pretence of amounting to mandatory law in the sense domestic or international law use it.

(b) The provisions of the PICC 2016 which are mandatory are normally expressly indicated as such, eg, Article 1.7 on good faith and fair dealing; the provisions of Chapter 3 on substantive validity (see Art 3.1.4); and Article 10.3(2) on limitation periods. Exceptionally, the mandatory character of a provision is only implicit and follows from the content and purpose of the provision itself (see, eg, Articles 1.8 and 7.1.6).