Banks issue letters of credit as a way to ensure sellers that they will get paid as long as they do what they’ve agreed to do. Letters of credit are common in international trade because the bank acts as an uninterested party between buyer and seller. For example, importers and exporters might use letters of credit to protect themselves. In addition, communication can be difficult across thousands of miles and different time zones. A letter of credit spells out the details so that everybody’s on the same page.