Instruments of credit refer to the various financial documents that facilitate the exchange of goods and services without the use of cash. These documents usually contain a promise to pay a certain amount at a later date. Two examples of instruments of credit are bills of exchange and promissory notes. A bill of exchange is a written order by one party to another party to pay a certain amount on a specified date. A promissory note is a written promise by one party to pay a certain amount to another party at a specified time in the future. Payment vouchers and statements of account are not instruments of credit, and billboards and postal stamps are not financial documents at all.