FIDIC合同一直是众多国家和多边银行经常使用的国际工程承包合同范本。特别是中国工程承包商常见的《施工合同条件》（Conditions of Contract for Construction），简称“新红皮书”。
FIDIC Conditions of Contract For CONSTRUCTION for Building and Engineering Works Designed by the Employer First Edition 1999
1.1.1.3 Letter of Acceptance 中标函
"Letter of Acceptance" means the letter of formal acceptance, signed by the Employer, of the Letter of Tender, including any annexed memoranda comprising agreements between and signed by both Parties. If there is no such letter of acceptance, the expression "Letter of Acceptance" means the Contract Agreement and the date of issuing or receiving the Letter of Acceptance means the date of signing the Contract Agreement. 中标函指雇主对投标文件签署的正式接受函，包括其后所附的备忘录(由合同各方达成并签定的协议构成)。在没有此中标函的情况下，“中标函”一词就指合同协议书，颁发或接收中标函的日期就指双方签订合同协议书的日期。
As with most signed documents one must undertake some due diligence to ensure that who is signing the document on behalf of the Employer has the authority to do so. It is important to ensure that the Letter of Acceptance matches the tender or, if there have been subsequent negotiations, an amended version of that tender. Otherwise, the Letter of Acceptance would be more like a counter-offer which would require a further acceptance from the Contractor before a contract was formed。 作为业主接受承包商投标函的唯一文件，承包商应当开展尽职调查，确保签字人能够代表业主进行此工作。同时，我们还需要确认中标函和投标函是相对应的，或者在后续谈判过程中对投标文件进行了修正。中标函更像是一个反要约，是承包商在合同签订前对投标函的进一步确认而已。
The importance of the drafting of the Letter of Acceptance is further heightened by the fact that it is second only to the Contract Agreement in the priority of documents contained at Sub-Clause 1.5. 其在Sub-Clause 1.5中文件的优先次序中仅次于合同协议书，重要性就不必多说了。
国内通常称之为中标通知书，国内很多法律文件也降其定义为中标通知书 。投标函是要约，中标函是承诺。中标函发出，即意味着要约承诺的法律过程生效，也即合同已经生效。
1.1.1.4 Letter of Tender 投标函
"Letter of Tender" means the document entitled letter of tender, which was completed by the Contractor and includes the signed offer to the Employer for the Works. 投标函指名称为投标函的文件，由承包商填写，包括已签字的对雇主的工程报价。
The Contractor must ensure that all of the documents which it intends to form part of its Tender are attached to the Letter of Tender otherwise any such documents will not form part of the Contractor’s Tender. The Letter of Tender is ranked number 3 in the order of priorities but it is very likely that many of the documents attached to the Letter of Tender will not be superseded by documents contained in the Letter of Acceptance or Contract Agreement. 承包商必须确保其拟作为其投标一部分的所有文件都附在投标书中，否则任何此类文件将不构成承包商投标的一部分。不符合招标文件格式的会导致废标。 在投标函按优先顺序排在第三位，但投标函所附的许多文件很可能不会被中标书或合同协议中包含的文件所取代。
投标函通常都是按招标文件中的要求和格式随商务标密封送达给业主的，可以简单理解不在“密封文件”内的一般都不能算投标函内容。对于招标澄清进行投标响应的澄清回复文件也是投标函的一种形式。
