近三十年以來，國際金融與質易實務上流行以履約擔保狀（performance bonds），擔保信用狀（standby credits）及銀行擔保狀（die Bankgarantie）等來作信用工具，以確保基礎（契約）關係所生義務之履行。此些信用工具雖在名稱與銀行實務上有所差異，但在法律性質上則屬相同，皆要求開狀銀行在擔保狀受益人提出狀上所載之單據（或甚至單純請求）時，向受益人給付狀上所載之金額（擔保金），而不得以基礎關係上有所爭執為由而拒絕給付。因此，本文以「擔保狀」一詞概括稱之。 擔保狀本其有「先付款再爭論」（Pay first, argue later; Erst zahlen, dann prozessieren）之功能設計，其目的在於使受益人提出狀上所載之單據時，能迅速而確定地自銀行獲得付款，等該擔保金在手之後，若擔保狀申請人欲請求返還該擔保金，再與申請人爭論基礎關係上之是非。為確保此一目的與功能的達成，擔保狀須獨立於基礎（契約）關係，而不容開狀銀行以基礎關係上之爭執為由而拖延給付擔保金，此乃擔保狀所具之獨立性原則所生之效用。 所謂擔保狀之獨立性原則乃指擔保狀及其所含之付款承擔是與其所擔保之基礎關係個別地存在，而且在通常情況下係獨立於該基礎關係而不受其影響。擔保狀開狀銀行的義務在於當擔保狀受益人提出符合狀上所載條件之文件時，兌現其付款承擔，而且此一義務並不以該受益人證明擔保狀申請人（例如基礎承攬契約之承攬人）真有違反其基礎關係上的義務為前提。因此，開狀銀行所關心者為：受益人所提出之文件（甚至是一單純請求）是否與擔保狀上所載條件相符，而非該基礎關係上所生之爭執是誰是誰非。與此一原則相呼應的另一原則是，開狀銀行所處理者為單據文件而非基礎關係所涉之商品、服務或履約與否之問題（或可稱之為單據原則）。然而，擔保狀之所以具有獨立性，並非僅因銀行所處理者為單據文件而已，而是因擔保狀交易之當事人有意使受益人於萬一基礎關係生變時有一迅速而確定地獲得付款的管道。 就擔保狀作為一個金融工具的功能圓滿性而言，獨立性原則具有舉足輕重的地位，因為擔保狀的簽發等於是將擔保金交給受益人，而欲確保此一付款管道的通暢，擔保狀須獨立於基礎（契約）關係所生的紛爭，而不允許開狀銀行以基礎契約有所爭執為由拒絕付款，亦不允許法院以命令禁止銀行付款（除非有構成獨立性原則之例外之事由發生），否則，此一流暢的付款管道將被阻塞。更何況，基礎契約的履行有所爭執，可謂十常八九，若申請人有權動輒以該爭執禁止開狀銀行付款，則擔保狀便未能給予受益人獲得擔保金的確定性，而終將造成無人願意接受擔保狀的後果。 然而所謂獨立性原則，其並不表示開狀銀行無論如何皆須兌現其付款承擔，而完全不得檢查受益人之請求在基礎契約中是否有所根據。若有明白證據足以證明受益人之請求在基礎契約顯無根據，則其請求在英國、美國法上將被認為具有欺騙性（fraudulent）；在德國、日本法上將被認為構成權利濫用。由於擔保狀交易常是一跨國交易，各國法律有加以統一協調之必要，而英國、美國、日本及德國等國家之法律，不但所使用之擔保狀之名稱不同，而且在獨立性原則之例外方面之論理架構亦不同，因此，本文探討了最常使用擔保狀之英國、美國、日本及德國之相關實體法與程序法規定，以了解有關獨立性原則及其權利濫用例外之現代發展與趨勢，俾供我國之借鏡。

Banks and other similar financial institutions perform important economic functions in global commerce now. Holding themselves out to be credit lenders, they substitute their credit standing for that of their customers by issuing payment undertakings, and their resources and integrity of management give the beneficiaries of their undertakings strong confidence. Documentary credits，standby credits，performance bonds and bank guarantees are well known examples of these undertakings. In this area of law, the use of terminology is confusing. The terms "performance bond", "demand guarantee", "performance guarantee", and "bank guarantee" have been used interchangeably to denote an independent guarantee, as opposed to an accessory guarantee. In addition, standby credits, which are distinct from independent guarantees only in practice and procedure, have been used widely. As a matter of fact, standby credits and independent guarantees both share the same legal characteristics, e.g., they are independent in nature and of a documentary character. Therefore, in this thesis the term "documentary guarantee" is used to denote both an independent guarantee and standby credit, while the term "documentary credit" denotes a commercial letter of credit or bankers' commercial credit. Documentary guarantees enable their beneficiary to have prompt and certain payment from a reliable paymaster, pending resolution of any underlying dispute with money in his pocket (the "pay first, argue later" function). In doing so, they exercise a risk allocation function. They shift the burden of litigation in that the beneficiary can rapidly have funds in hand by way of presenting conforming documents, and it is the account party that has to start proceedings if he wishes to reclaim that money. They also shift the forum of litigation in an international transaction in that the account party has to approach the beneficiary in his country to start an action there. All of these functions are predicated on the principle of independence of documentary guarantees. This principle means that the payment undertaking contained in a documentary guarantee is separate from, and in the ordinary way independent of, the underlying contract giving birth to it. What the issuer is concerned with is whether the tendered documents, or even a simple demand, comply with the terms and conditions of the undertaking, rather than with the disputes arising from the underlying contract. But the principle of independence does not mean that the issuer is in all cases required to honour a demand for payment. In a clear case of the beneficiary's fraud (or abuse of right), the issuer is entitled, and is obliged, to refuse to pay, not only because there is as much public interest in discouraging fraud as in encouraging the use of documentary guarantees, but also because the beneficiary's fraud is not within the risk that has been distributed to the account party by the use of documentary guarantees. Thus, the fraud exception (or the abuse of right exception) is recognized worldwide. Fraud, however, must be clearly proved before it can be used as a defence by the issuer against the beneficiary; the account party, in the case of clear fraud, also can apply for an interim injunction to restrain the beneficiary from making a fraudulent demand, or to enjoin the issuer from making payment. This thesis discusses the substantive aspect of the fraud exception, and explores the procedural difficulties concerning a fraud allegation. Reference will be made to English law, American law, and German law in order to identify the modern trends and developments in this area of law.