in law, behaviour that contributes to one's own injury or loss and fails to meet the standard of prudence that one should observe for one's own good. Contributory negligence of the plaintiff is frequently pleaded in defense to a charge of negligence.

Historically the doctrine grew out of distrust of juries, which have usually been more sympathetic to plaintiffs in personal injury lawsuits. The policy of not apportioning liability between parties to lawsuits (that is, charging each with some fraction of the blame) also encouraged the doctrine.

Contributory negligence usually arises in a lawsuit in which a plaintiff has accused a defendant of negligence. The defendant may then charge the plaintiff with contributory negligence. At common law, if the defendant proves this charge by a preponderance of evidence, the plaintiff cannot recover any damages—even if the defendant was negligent—because the contributory negligence breaks the causal connection between defendant's negligence and plaintiff's injury or loss. In English law since the Law Reform (Contributory Negligence) Act (1945) and in many states in the United States, if the plaintiff is shown to have contributed to the injury, recovery may still be allowed, but provision is made for an equitable reduction of damages.

Contributory negligence should be distinguished from several other doctrines often applied in negligence cases: assumption of risk, which relieves the defendant of an obligation of due care toward the plaintiff when the latter voluntarily exposes himself to certain dangers; last clear chance, which allows the plaintiff to recover even though contributorily negligent—if the defendant had the last clear chance to avoid the mishap.

Contributory negligence is criticized by some authorities because it excuses one party (defendant) even though both were negligent. One solution is loss apportionment—charging both parties when both were at fault. This practice operates in maritime law in Canada and Australia and in most civil-law countries (e.g., France and Germany). See also negligence.