The study of the supplementary nature of the unjustified enrichment should be based on defining what is the supplementary nature of the unjustified enrichment?How does it form? What is the effect? And, is that legitimate for the unjustified enrichment with the nature of supplementary? The first part of this study attempts to define the supplementary nature of the unjustified enrichment and to limit the range in consideration of giving prominence to the true nature of supplementary. The second part focuses on reconstructing the historical causes and analyses among the most influential countries in the past history about the unjustified enrichment, France and Germany. The third part analyses the discrepancies mentioned between two countries to find out the basic causes of various approaches and influences exercised over the issue of the competition on the unjustified enrichment. The fourth part of this study is to be aimed at the spread and succeed of both the doctrine and legislative dimensions about the supplementary nature of the unjustified enrichment, to do an independent analysis on Latin law. The fifth part goes further on the legislative basis of the supplementary nature of the unjustified enrichment, to integrate omnigenous opinions of support or oppose, and attempts to address a complete and rational theory to in accordance with the legislative basis about the supplementary nature of the unjustified enrichment.

本文要研究的是不當得利補充性，因此整個研究就是要尋找：什麽是不當得利的補充性？它是如何形成的？其後果如何？以及要求不當得利具補充性質是否合理。 本研究的第一部分嘗試尋找不當得利補充性的定義，從而限定補充性的範圍，突出真正的補充性質。 第二部分致力於重構不當得利產生的歷史原因。其中，尤其是不當得利歷史沿革進程影響最大的法國法與德國法作出分析。 第三部分嘗試就法國法與德國法的上述差異作出分析，找出它们取向不同的基本成因，以及所產生的影響。 第四部分針對拉丁法系就不當得利補充性相關的各種學說與立法方面的繼受作出分析研究。 第五部分綜合各種支持和反對意見，嘗試提出一套既完整又合理的學說理論，作為支持不當得利補充性的立法依據。