Negligence per se is a doctrine that provides that if a person is negligent while violating a related law or regulation, the person is negligent, or a presumption is created that the person is negligent. Negligence per se allows a plaintiff to prove the breach of duty element in a negligence case.

For example, let’s say that there is a car accident between car A and car B. A sues B for negligence. A is able to prove that B was driving 20 miles over the speed limit. The fact that B exceeded the speeding law—a safety regulation—probably establishes that B was negligent per se.