In criminal law, strict liability is liability for which mens rea (Law Latin for "guilty mind") does not have to be proven in relation to one or more elements comprising the actus reus ("guilty act") although intention, recklessness or knowledge may be required in relation to other elements of the offense. The liability is said to be strict because defendants could be convicted even though they were genuinely ignorant of one or more factors that made their acts or omissions criminal. The defendants may therefore not be culpable in any real way, i.e. there is not even criminal negligence, the least blameworthy level of mens rea.

Strict liability laws were created in Britain in the 19th century to improve working and safety standards in factories. Needing to prove mens rea on the part of the factory owners was very difficult and resulted in very few prosecutions. The creation of strict liability offenses meant that convictions were increased. Common strict liability offenses today include the selling of alcohol to underage persons and statutory rape.

These laws are applied either in regulatory offenses enforcing social behaviour where minimal stigma attaches to a person upon conviction, or where society is concerned with the prevention of harm, and wishes to maximise the deterrent value of the offense. The imposition of strict liability may operate very unfairly in individual cases. For example, in Pharmaceutical Society of Great Britain v Storkwain, a pharmacist supplied drugs to a patient who presented a forged doctor's prescription, but was convicted even though the House of Lords accepted that the pharmacist was blameless. The justification is that the misuse of drugs is a grave social evil and pharmacists should be encouraged to take even unreasonable care to verify prescriptions before supplying drugs. Similarly, where liability is imputed or attributed to another through vicarious liability or corporate liability, the effect of that imputation may be strict liability albeit that, in some cases, the accused will have a mens rea imputed and so, in theory, will be as culpable as the actual wrongdoer.