When a person is injured by a dangerous or defective product they are often entitled to compensation for their pain and suffering. Such cases are referred to as "product liability" cases, and they can be successful even if the defect was not the fault of the manufacturer. The key is whether the product was "unreasonably dangerous" when it entered the "stream of commerce". The generally accepted legal test for "unreasonably dangerous" is whether the product "failed to perform in a manner reasonably to be expected in light of its nature and intended function". Often this means there was a production or design flaw, but not necessarily. A product liability case may be appropriate if the item worked as it was supposed to, but the manufacturer failed to include sufficient warnings or instructions on how to use it safely. A key difference between products liability and traditional negligence is that plaintiff's negligence is not a defense, so long as the product was used in the way it was intended to be used. However, if it can be shown that the plaintiff knew that the product was likely defective and used it anyways (for instance, taking expired medication), the defendant will prevail.

In order to win a lawsuit for Product Liability, a plaintiff must establish:

1. A defective product was placed in the stream of commerce by one in the business of selling products.
2. The product is defective and unreasonably dangerous, either by a defect in design or a failure to warn of dangerous properties.
3. The defect existed when the product left the defendant’s control.
4. The defect proximately caused injury to a person or property.