“restitutionary claim”指的是返还请求。返还请求权，是指权利人对无权占有或侵夺其物的人，有权请求其返还占有物。该项请求权是由所有权所派生的请求权，并且是所有权效力的直接体现，只要他人无权占有或侵夺权利人的财产，权利人都可以通过行使该项请求权而恢复其物权的圆满状态。Restitution involves the court, as part of a sentence in a criminal case, ordering a defendant to compensate the victim for losses suffered as a result of the crime. All states have laws providing that convicted defendants pay restitution to their victims.

“返还请求权”与合同法、侵权行为法并称为当代英美债法的三大支柱，而“unjust enrichment”则是“返还请求权”的基础。

“unjust enrichment”不当得利

指既非赠与也无合法理由而从他人处获得的利益，对此，受益人须返还原物或给予补偿。但是，英国法采纳不当得利返还原则的程度究竟有多深是值得怀疑的，因为在英国法中多以返还原物〔restitution〕这一术语替代之。在罗马法和苏格兰法中，不当得利返还原则则是以准合同之债〔quasi-contractual obligation〕为基础的，受益人负有返还义务。这也是海商法中海难救助与共同海损之债的基础理由。以不当得利为基础的请求权应具备下列三个要件：１被告得到了原告的利益；２被告对此利益有所识别和了解；３在当时的情况下，被告无偿接受和保留该利益是不公平的。In laws of equity, unjust enrichment occurs when one person is enriched at the expense of another in circumstances that the law sees as unjust.[1] Where an individual is unjustly enriched, the law imposes an obligation upon the recipient to make restitution, subject to defences such as change of position. Liability for an unjust (or unjustified) enrichment arises irrespective of wrongdoing on the part of the recipient. The concept of unjust enrichment can be traced to Roman law and the maxim that "no one should be benefited at another's expense": nemo locupletari potest aliena iactura or nemo locupletari debet cum aliena iactura.

以下为相关双语示例，供参考：

The Arbitral Tribunal finds that Claimant is also not entitled to the payment of EUR 425,00.00 as “losses calculated on the basis of the missing license fees” based on unjust enrichment and the legal bases referred to by Claimant in this regard (Sections 1311, 1041, 1431 ABGB),298 as the latter are extra-contractual and, as such, do not provide a basis for claiming expected contractual returns (which are governed by Article 5.3 of the August Agreements, providing that “XXX will 

receive license fees for first 7500 units produced by eKontrol” (emphasis added)

仲裁庭认为，申请人也无权基于不当得利和申请人在此方面提到的法律依据（《奥地利民法》第1311条、第1041条和第1431条）[ 例如，见申请人庭后简述第400段等。]要求赔偿425,00.00欧元“许可费损失”[ 仲裁通知第66段。]，因为不当得利与合同基础相抵触，不能基于此请求支付预期合同收益（受制于八月协议第5.3条的规定：“XXX还将就YYY生产的首批7,500台装置收取许可费”（重点强调）。