A promissory note is also a negotiable instrument, similar to a bill of exchange, except that there are only two parties.

A 'Promissory note' is an unconditional promise in writing made by one person to another signed by the maker, engaging to pay, on demand at a fixed or determinable future date a sum certain in money to, or to the order of, a specified person or bearer.

Promissory notes are widely used as debt instruments, for example in long-term projects containing numerous stage payments, where a buyer or borrower issues one or more promissory notes promising to pay a specified amount on a stated due date.

When a promissory note is not paid when due, then special procedures in some countries require
that the promissory note be ‘noted’ or ‘protested’ for non-payment, to preserve the holder’s legal rights. It is common that within 24 hours of an indication of non-payment or non-acceptance, a notary public
or similar person must be asked to demand acceptance or payment and then write the reason for non-payment or non-acceptance on the promissory note. Protest for foreign bills may be done later and is a more formal record of non-payment or non-acceptance. Failure to comply with local requirements can result in the drawer (and any endorsers) being absolved from liability to pay.

Protesting a bill of exchange may indicate an act of bankruptcy in some countries, and the implications of this should be considered before such instructions are given.