公共工程因具有工期長、配合地型及設計……等複雜因素，導致施工過程經常會因各種因素而造成超出預定時程之情形，根據英國的實證研究顯示，政府採購的履約爭議（訴訟或仲裁）中，工期爭議是最常見的爭議。我國隨著政府採購法施行十餘年，設立採購申訴審議委員會以來，其中調解案之大宗亦以工期有關爭議為最多，由此可見在公共工程中工期認定在履約程序中之重要性。關於公共工程契約之工期爭議，如拉長時間軸之後，吾人發現關於公共工程工期展延，有兩個歷史轉折，第一：是關於機關展延工期核准權之實務變遷，從過去機關依合約握有工期展延核可之絕對裁量權，變遷至現在一旦有客觀不可歸責於廠商之事由致延長工期時，機關即應予展延工期，不再有過去之絕對裁量權。第二：過去之工期爭訟案件中廠商態度較消極，廠商提起訴訟大多只要能獲得展延工期而不必計罰即可，然而現在廠商態度轉趨積極，在工期爭議提起之訴訟中（或調解、仲裁），不但要求展延工期還要機關給付展延工期所增加之管理費及必要支出。本文將對於公共工程中最常見之工期爭議中之三大爭議問題，包括：「履約期間之計算」、「機關核可權」、以及「展延工期補償之請求權基礎」等三大議題加以探討，其中尤以第三個議題－請求補償之法律上請求權基礎何在？實務裁判上，就此法律問題衍生出高達十餘種不同之法律上之請求基礎，令人眼花潦亂，本文亦將逐一介紹這十餘種展延工期請求權基礎之各自立論依據，希望能有助於政府部門日後執行公共工程時得以減少法律爭議而順利執行。

Public construction involves complex factors such as the long construction period, landform mapping and design, which usually lead to the situation, where the construction process goes beyond the anticipated duration. As shown in an English study, in the process of contract disputes on government procurement, the construction duration dispute is the most common one. Since the Nation enacted the Government Procurement Act and established the complaint review board for government procurement over ten years ago, disputes related to construction duration have accounted for the most of the reconciliation cases. To this end, the duration of public construction is critical in the process of carrying out contracts. In relation to the duration dispute of public construction contract, such as extending the time, the author found two historical transitions. The first transition is related to the practical change of government agencies' permission of extending the construction duration. In the past, government agencies based on the contract held the right of discretion for the approval of time extension. Different from the past, government agencies at present can approve the extension of the construction duration, which is caused by objective reasons that are not attributed to the companies. Secondly, in the past, companies' attitude for litigation cases related to the construction duration was passive. It was okay for companies who instituted a litigation to gain extension of the construction duration and get no fine. However, companies' attitude at present becomes active. In the process of litigation related to construction duration disputes, not only do companies request time extension, but they also request government agencies pay the additional management fee and necessary expense for the extended period. This article focuses on the three biggest issues in relation to most common public construction duration disputes, including: 'calculation of the contract performance period', 'permission by government agencies' and 'the basis of claim rights to compensate for extension of the construction duration'. In particular, what is the basis of claim rights for compensation in a legal sense? Judging from a practical perspective, this legal issue brings about more than ten different bases of legal claim rights. This article will introduce the individual arguments on which the more than ten kinds of claim rights for the construction period extension are based. It is to be hoped that this article will be of help for the government agencies in terms of reducing legal disputes when implementing public construction.