Which contracts must be signed in writing?

Written form is not a necessary condition for the contract to take effect. A contract can be concluded in written or oral form, and a contract reached through oral agreement is also established unless it is required by law to be in written form. The form of the contract, that is, the expression of the contract, as the carrier of the will of the parties, has certain influence on the effectiveness of the contract. The form of contract can be divided into written form, oral form and other forms. If the written form is stipulated by laws and administrative regulations or agreed by the parties, it shall be in writing. Written form refers to contracts, letters and data messages (including telegrams, telexes, faxes, electronic data interchange and e-mails) and other forms that can tangibly express the content. It should be noted that a contract that should be concluded in writing but not in writing cannot be considered invalid. According to the spirit of legislation, the requirement of written form of contract is mainly based on the consideration of evidence, so as to solve such contract disputes more easily. In other words, "should" and "must" here are different. Even if it should be in writing and not adopted, if one party fulfills its main obligations and the other party accepts it, the contract is also established. Legal basis: Article 10 of the Contract Law of People's Republic of China (PRC) Contract can be in written form, oral form and other forms. If laws and administrative regulations stipulate that it should be in writing, it should be in writing. If the parties agree to use written form, it shall be in written form.