A cancellation letter is a formal document used to terminate a subscription, membership, service, or agreement. It should be concise, respectful, and include key details such as your full name, contact information, account or membership number, and the specific service you wish to cancel. Clearly state your intention to cancel, provide the effective cancellation date, and request written confirmation. Optional sections can include a brief reason for the cancellation and a note of appreciation for the service received. Always keep a copy of the letter for your records.