Bidding is a way of contract conclusion. Therefore, we should understand the legal issues in bidding from the general principles of contract conclusion.
　　
(1) General principles of contract conclusion. A contract is the result of agreement between the parties. The conclusion of a contract generally goes through two stages: offer and acceptance. An offer is an expression of intention made by one party to the other party that it is willing to enter into a contract with the other party under certain conditions, and contains binding force on the party making the offer once it is accepted by the other party. The party who makes a summary offer is called the offeror, and the other party becomes the offeree. An effective offer must meet the following requirements: ① The offer must indicate the offeror's intention to enter into a contract with the other party in accordance with the conditions set forth in the offer. ② The content of the offer must be clear and definite, that is, it should include the main conditions of the contract to be signed. Once the offeree expresses its acceptance, it is enough to form a contract binding on both parties. ③ An offer must be communicated to the offeree before it becomes effective. The binding force of an offer includes two meanings: one is the binding force on the offeror, the other is the binding force on the offeree. The binding force of an offer on the two is different. Generally speaking, an offer is not binding on the offeree. After receiving the offer, the offeree has only acquired the right of acceptance in law, but is not bound by the offer and does not assume the obligation of acceptance. Moreover, under normal circumstances, the offeree has no obligation to notify the offeror even if it does not accept. The so-called binding force of an offer on the offeror refers to whether the offeror can renege, change the contents of the agreement, or revoke the offer after sending the offer and before the other party accepts it. This problem mainly arises in the period from the time when the offer has reached the offeree to the time when the offeree makes an acceptance. In law, an offer should be distinguished from an invitation to offer. Invitation to offer, also known as solicitation of offer, although its purpose is also to conclude a contract, it is not an offer in itself but to invite the other party to make an offer to itself. The main difference between an offer and an invitation to offer is that if it is an offer, once it is accepted by the other party, the offeror must be bound and the contract is formed; In the case of an invitation to offer, even if the other party fully agrees or accepts the conditions set forth in the invitation to offer, the party who sends the offer is still not bound, and the contract cannot be formed unless he expresses his acceptance or confirmation. An acceptance is the offeree's consent to the contents of the offer in the manner specified in the offer. The contract is formed when the offeror receives the acceptance.
　　
(2) The legal nature of bidding. The purpose of bidding is to select the winning bidder and sign a contract with it. Therefore, bidding is a specific act of signing a contract and a special form of offer and acceptance. The main specific legal acts in bidding include bidding, tendering and determination of the winning bidder. ① The legal nature of bidding is invitation to offer. According to the general principle of contract conclusion, the direct purpose of the tenderee to issue the tender notice or invitation to bid is to invite the bidder to bid, and the bidder does not necessarily have to sign a contract after bidding. Therefore, the bidding act is only an invitation to offer, and generally has no legal binding force. A tenderer may modify the tender announcement and tender documents. In fact, all international government procurement rules allow clarification and modification of bidding documents. However, due to the particularity of the bidding behavior, in order to achieve the principles of efficiency and fairness in procurement, the procurement agency often needs to follow some basic principles when modifying the bidding documents. For example, all international government procurement rules stipulate that the modification should be carried out within the bid validity period, and all bidders should be provided with the same modification information, It is not allowed to discriminate against the bidder in this process. ② The legal nature of bidding behavior is offer behavior. The bidding document contains specific terms for concluding a contract in the future, and the contract can be signed as long as the bidder promises (declares winning the bid). The tender act as an offer is legally binding, which is reflected in that the tender is one-time, and the same bidder cannot submit more than one tender for the same tender; Each investor is responsible for its own quotation; During the bid validity period after the bid document is issued, the bidder shall not modify the contents of the bid document or withdraw the bid document at will. ③ The legal nature of the bid winner's behavior is determined as commitment behavior. Once the procurement agency announces the determination of the bid winner, it is a commitment to the bid winner. Both the procurement agency and the winning bidder have the right to ask the other party to sign a contract, and also have the obligation to sign a contract with the other party. In addition, both parties cannot negotiate on the contents of the contract until the bid winning result is determined and the contract is signed.