International Contract Law presently offers three sets of principles: the UNIDROIT Principles of International Commercial Contracts (the UNIDROIT Principles), the Principles of European Contract Law (the PECL) and the Draft Common Frame of Reference (the DCFR). These sets of principles contain general principles which are intended to serve as model rules. The three sets of principles have been published, but they have not been adopted. The UNIDROIT Principles and the PECL are not meant to be adopted either. There are different opinions as to whether the sets of principles can be considered to be a source of legal status at all.

The sets of principles have been referred to in Swedish law. Swedish case law – in which the principle collections are mentioned – serves as guidance to when these sets can be expected to be part of Swedish law since the UNIDROIT Principles, the PECL and the DCFR not are regulations.

Four cases from the 21^st century have been found in which the sets of principles have been mentioned. A principle from the DCFR was applied by the Swedish Supreme Court in the case NJA 2009 s. 672 – which was one of the four cases that were found. An analysis was made in order to identify similarities and differences as to when the UNIDROIT Principles, the PECL and the DCFR previously have been mentioned in Swedish case law.

It has been difficult to find similarities in the four cases that were found. Neither the form of contract, the contract-type, nor the presence of any international dimension in the proceedings were common denominators. One common denominator was however the Justice Council named Torgny Håstad. Håstad being one of the judges in each of the four cases – he was also one of the judges in the case NJA 2009 s. 672. It is particularly noteworthy since Håstad has been involved in the European project which resulted in the DCFR.

The absence of a clear pattern on when the principle collections are mentioned in Swedish case law shows that the legal certainty might be at risk. The legal certainty is endangered since it in present time seems to be necessary to see to which judges and referees are ruling in the case and their respective personal attitude towards the UNIDROIT Principles, the PECL and/or the DCFR.