A promissory note is a written unconditional promise by one party (the maker) to pay another party (the payee) a specified sum of money. It must be in writing, signed by the maker, specify the amount to be paid, and have a definite payee. There are two parties to a promissory note - the maker who promises to pay the amount, and the payee who is owed the money. A promissory note is a negotiable instrument if it meets additional requirements of being an unconditional promise to pay a certain sum on demand or at a definite future time.