A manufacturing defects may occur in the construction or production of a product. A product has a manufacturing defect if (1) it differs from the manufacturer’s design or specifications (the product departs from its intended design) making it more dangerous than consumers expect it to be; and (2) the products that were manufactured or produced differently are from the same manufacturer and were intended to be identical.

Although manufacturing defects are relatively uncommon, if a product has a manufacturing defect, the manufacturer will be strictly liable in tort for damages caused by the defective product. This means the manufacturer will be liable even if the manufacturer exercised great care in manufacturing the product and was not negligent.

Products liability laws vary from state to state and may be in a state’s statutes or in its court opinions (also known as case law or common law).

In Illinois, the concept of strict liability applies to cases involving manufacturing defects. Under this legal principle, if a product has a manufacturing defect—meaning it deviates from the manufacturer's intended design or specifications and is more dangerous than consumers would expect—the manufacturer can be held strictly liable for any resulting damages. This is true even if the manufacturer took all possible care in the production process. Illinois law does not require the injured party to prove negligence on the part of the manufacturer; it is enough to show that the product was defective and that the defect caused the injury. This approach is consistent with the state's aim to protect consumers from unsafe products and to ensure that manufacturers bear the responsibility for the integrity of their products. The specific application of these principles can be found in Illinois statutes and reinforced by case law.