A letter of credit is a written undertaking by an importer's bank, known as the issuing bank, to pay the exporter, or beneficiary, a specified amount of money within a set time limit if certain documents are presented. There are different types of letters of credit, including irrevocable and revocable, confirmed and unconfirmed, transferable, standby, and revolving letters of credit. The key parties involved in a letter of credit transaction are the applicant, issuing bank, beneficiary, advising bank, confirming bank, negotiating bank, and reimbursing bank. Required documents to be presented under a letter of credit usually include bills of exchange, invoices, transport documents, insurance documents, and various certificates.