公法上不當得利制度於建制之初，大量援引民法不當得利之概念作為內涵，使兩制度之根源存在若即若離的緊密關係。隨著公法上不當得利之法理基礎、制度內涵漸次成熟完備，對於往昔援引民法不當得利作為補充之模式，應漸有反省之思維。在多人關係之公法上不當得利案型，如何在債權人、受益相對人（即第一利益受領人）與利益轉得之第三人（即第二利益受領人）間，擇定返還義務人與確定利益返還範圍，尤凸顯公法與民法上不當得利制度之界分難題。而在建構公法上不當得利三方法律關係之權利義務時，究竟應溯源自民法不當得利概念，抑或應探尋公法上既有之制度機制？本文爰聚焦於此，嘗試釐清給付型之公法上不當得利三方權利義務關係。

The unjust enrichment system in public law at the beginning of the establishment of the system used many concepts of unjust enrichment from the civil law as its connotation. Hence the roots of the two systems are closely related. However, as the legal basis and institutional connotation of the unjust enrichment in public law gradually become more mature and complete, there should be a reflective thinking about citing previous cases from the civil law as the unjust enrichment supplementary model. In the case of unjust enrichment in the public law of multi-person relations, questions such as how to determine the return obligation between the creditor, the beneficiary counterpart (i.e., the recipient of the first interest) and the third party (i.e., the recipient of the second interest), and how to determine the scope of return of the interests and its transfer particularly highlight the difficulties of dividing the unjust enrichment system between public law and civil law. Moreover, when constructing the rights and obligations of three-party legal relations of unjust enrichment in public law, it inevitably invites the question of whether or not it shall be traced back to the concept of unjust enrichment in civil law, or it shall alternatively explores the existing institutional mechanisms in public law. This article focuses on these issues and attempts to clarify the relationship between the rights and obligations of the three parties of the unjust enrichment in public law.