Four types of letters of credit include: - Irrevocable Letter of Credit: Cannot be altered or canceled without the consent of all parties involved. - Revocable Letter of Credit: Can be altered or canceled by the issuing bank without notice. - Confirmed Letter of Credit: Involves a second bank (confirming bank) providing a guarantee of payment in addition to the issuing bank's obligation. - Standby Letter of Credit: Used as a backup payment method if the applicant fails to fulfill its financial obligations.