Most consumer purchases are covered by a warranty, even when it is not explicitly stated as such. The two main types are express and implied warranties. An express warranty is one that is clearly stated (or "expressed") either verbally or in writing, while an implied warranty automatically covers most consumer goods valued over a certain amount, but only provides a base level of protection for consumers.
The following information serves as a primer for these two distinct types of warranties. See Consumer Warranty Basics, What Does 'Caveat Emptor' Mean?, and What Will Void a Warranty? for more details.
An express warranty can take several different forms, whether spoken or written, and is basically a guarantee that the product will meet a certain level of quality and reliability. If the product fails in this regard, the manufacturer will fix or replace the product for no additional charge. Many such warranties are printed on a product's packaging or made available as an option.
A verbal express warranty may be as simple as a car dealer telling a customer, "I guarantee that this engine will last another 100,000 miles." If the car fails to live up to this claim, the buyer may take it up with the seller (although proving the existence of a verbal warranty is very difficult).
Other warranties may be expressed in writing but do not necessarily look like traditional warranties. For example, a light bulb manufacturer prints the words "lasts 15,000 hours" on its packaging. The words "guaranteed" or "warranty" do not appear, but this claim nevertheless is an express warranty.
Most consumer purchases are covered by an implied warranty of merchantability, which means it is guaranteed to work as claimed. For instance, a vacuum cleaner that does not create enough suction to clean an average floor is in breach of the implied warranty of merchantability. Federal law defines "merchantable" by the following criteria:
Even used goods are covered, although some states allow retailers of either used or new goods to invalidate the implied warranty by stating "sold as is."
Products guaranteed for a different purpose than what the manufacturer explicitly intended come with an implied warranty of fitness. For example, if a shoe salesperson sells you a pair of high heels for running -- assuming you've made it clear that you want shoes for running -- then your purchase is covered under an implied warranty of fitness.
See What is an Implied Warranty? for more details.