Product liability law is a law that holds companies liable for harm caused by defective products. Generally the manufacturer or seller of a defective product will be held liable as long as the defect existed at the time the product left control of the party. Additionally, there is a general requirement that the defect must have caused the harm to the consumer while the consumer was using the product in a reasonably foreseeable manner. Modern product liability theory places strict liability on manufacturers and sellers for harm caused by defective products — i.e., the consumer does not have to show that the manufacturer or seller was negligent in order to recover for harm suffered.
Under product liability law, the product must have been defective at the time it left the control of the manufacturer or seller. For example, if a consumer purchases a riding lawnmower that has a defective blade at the time of purchase and is subsequently injured by that blade, she could recover under product liability law. However, if the same consumer makes a modification to the lawnmower after purchasing the item, causing the blade to come loose and cause injury, then neither the manufacturer nor the seller may be held liable for the harm.
The harm to the consumer must have occurred while the product was being used in a manner that is reasonably foreseeable in order for the consumer to recover for the harm suffered under product liability law. Continuing the previous example with the riding lawnmower, there may arise a scenario in which the consumer drives the mower down a rocky dirt road and the blade hits a rock, breaks off, and cuts her leg. If the court finds that driving the mower down the road is not a reasonably foreseeable use, then the consumer will not recover under product liability law.
Modern product liability law in most jurisdictions has eliminated the requirement that a harmed consumer prove that the manufacturer or seller of the product was negligent. Rather, the manufacturer or seller is typically held strictly liable for such harm. The rationale behind this concept is that the individual consumer should not have to bear the risk of the product being safe when it leaves the manufacturer or seller.