An iou is valid as long as the borrower signs it himself, and it does not necessarily need the signatures of both borrowers and borrowers. It is best for borrowers to write IOUs by hand, but pay attention to the writing norms. Printed IOUs have the same legal effect, but they are easy to forge. The borrower's signature should also be thumbprinted. The borrower's information must be clearly written with the ID number, and the borrower should be required to provide the original for verification when writing the loan. In order to have legal effect when writing IOUs, we should pay attention to the following matters:

1. It is best for borrowers to write IOUs by hand, but pay attention to the writing standards.

2. The date of borrowing-be sure to write it clearly, preferably accurate to the day.

3. The loan amount should be capitalized in Arabic numerals and Chinese at the same time, and the currency should be clearly written to prevent the loan holder from tampering.

4. Payment shall be made by bank transfer as far as possible, and the account number and transfer date of the other party may be indicated on the debit note.

5. If the borrower is married, it is better to obtain the signature of the spouse, which is more secure for the creditor, and avoids that one party refuses to undertake the repayment obligation on the grounds of ignorance or one party transfers the property to the spouse when the court executes it, resulting in inability to repay.

6. After the IOU is issued, a copy of the borrower's autographed ID card and a copy of the marriage certificate shall be collected at the same time.

7. If the amount is large, you can ask a lawyer or a third party to witness and sign it.