A Letter of Warranty is a document attesting to the soundness and warranties of quality provided by a seller in regard to a service or product. It is generally used when selling goods or providing services involving costly investments over long periods. A Letter of Warranty provides assurance to a buyer that the goods or services they are purchasing will meet certain standards, such as accuracy, compliance, quality, merchantability, reliability, performance, and durability. The warranty may also specify a period within which any necessary repairs or replacements must be completed in the event that the goods or services do not perform according to expectations.