A warranty is a product manufacturer or service provider's documented guarantee of quality as promised to a customer.

Warranties provide customers with legally-ensured service replacement or correction of issues insofar as the warranty stipulates in its conditions, for the duration of its term. A warranty's term generally commences at the date of delivery or provision. The document stipulates what is guaranteed and what repairs or remediations will be performed to ensure the promised quality of the service or good, failing these conditions.

Warranties commonly cover defects in workmanship but may also cover physical abuse. Support service for products may also be covered by warranty, ensuring not only that a product functions as intended but that the customer has assistance in understanding its operation.

A good warranty of sufficient term and backed by quality service helps ensure buyer confidence, fosters good customer relationships, promotes the sellers brand and as a rule, improves sales.