The common law of products liability traditionally posits three major theories of liability: defectively manufactured products; defectively designed products; and those rendered defective because of absent or inadequate warnings. Thus, it is routine to speak about manufacturing defects (i.e., where the product does not conform to the manufacturer’s own specifications); design defects (where the product was made as intended but the design itself is being impugned because it has blameworthy shortcomings); and failure-to-warn claims (where warnings, directions or instructions to the consumer fall short, creating an injury).

Some states have codified aspects of products law so that the common law has been adopted or modified by statute. Causes of action such as negligence, strict products liability and breach of warranty are recognized vehicles by which to assert the defect categories. Despite some variations in state laws, it is the applicable state law that normally governs the substantive course of the products lawsuit.