我國民法總則編第一章命名為「法例」，而第一條規定：「民事，法律所未規定者，依習慣；無習慣者，依法理。」本條規定習慣作為法律以外，處理民事關係之第二順位法源。然而，習慣一詞，除出現在民法第一條外，尚見於其他條文（如第六八、一六一及二○六條等等）。究竟民法中所稱之習慣，其所代表之意義為何？其所生之效力又為何？又實務上就習慣在具體適用之狀況為何？本文因篇幅關係，擬僅就民法第一條所規定之習慣與債編所規定之習慣在學理及實務適用之情形作一分析，至於民法債編以外之物權編、親屬編及繼承編之習慣，則不在本文之探討範圍內。

Chapter One General Principles of the Civil Code named as Application Rules, and the article 1 in Civil Code of Taiwan defines, If there is no applicable act for a civil case, the case shall be decided according to customs. If there is no such custom, the case shall be decided according to the jurisprudence. In accordance with the provisions of article is custom treated as second source of law, to deal with civil legal relations. However, custom, in addition to the first article appeared in the civil code, but still found in other provisions (such as Article 68, 161 and 206 etc.). What means custom in civil law? What is legal effect of custom in civil Law? What is the application of custom in legal practice? In this paper is Research Focus based on a theoretical analysis and practice in the application of case about custom of article 1 und Obligation in Civil Code. Rights in Rem, Family and Succession in Civil Code are not to discuss in this paper.