There are 3 main methods of payment in international trade: clean payment, collection of bills, and letters of credit. Clean payment involves direct handling of documents between trading partners with a limited role for banks. It offers a cheap option but the exporter assumes risks. Collection of bills involves banks handling documents with options for release against payment or acceptance. Letters of credit are a written undertaking from the importer's bank to pay the exporter up to a stated amount against stipulated documents, and can be revocable or irrevocable, for sight or time, and confirmed.