a. Parties to international contracts need to be able to rely on their agreement. Therefore, they need to know whether there are any formal requirements that have to be met for their agreement or its amendment to be valid. Some jurisdictions ask for specific form or comparable requirements to be met for the validity of commercial sales contracts, whereas most legal systems opt for the rule of consensualism (i.e., freedom of form).

During the deliberations of UNCITRAL on the elaboration of the CISG, one of the most controversial issues at the Vienna Conference was whether or not the principle of freedom of form of Article 15 ULIS should be incorporated into the text of the CISG. Finally, a compromise was adopted with freedom of form as a basic rule and the reservation clause of Articles 12 and 96 CISG. Where at least one of the parties to the contract has its place of business in a reservation State and a court of that State hears the case, the court must determine the law applicable to form according to its conflict of law rules, just as a court of another State, which did not adopt the CISG, would have done.

Although the issue of freedom of form might as well have been regulated in Part II of the CISG dealing with the formation of the contract, it has been integrated as a general provision.