Volenti non fit injuria -- "to one who consents, no injury is done" -- is a defence in the law of torts that bars a claimant from recovering damages for harm to which the claimant freely and knowingly consented. The defence rests on the idea that a person who voluntarily accepts a known risk cannot later complain of the harm that risk actually produces.

Two elements must both be established for the defence to succeed. First, the claimant must have had actual knowledge of the specific risk involved, not merely a general awareness that some risk exists; consenting to a risk one does not actually understand is not genuine consent to that risk. Second, the claimant's acceptance of the risk must have been entirely free and voluntary, given without any form of compulsion, whether physical, economic, or arising from the claimant's employment relationship with the defendant.

The defence does not apply in several recurring situations. It does not extend to a risk created by the defendant's own negligence going beyond what the claimant actually consented to -- consenting to the ordinary risks inherent in an activity is not consent to a defendant's own careless conduct that creates a materially greater or different danger. It also does not apply where the claimant's apparent consent was not truly free, such as where an employee accepts a risk only because refusing would mean losing their livelihood, since consent given under economic necessity of this kind is not treated as genuinely voluntary. Nor does the defence apply where the claimant, though aware of a general danger, had no actual knowledge of the specific risk that in fact caused the harm.

Where volenti non fit injuria is successfully established, it operates as a complete defence, barring the claim entirely rather than merely reducing the damages recoverable, since it denies that any actionable wrong occurred at all once genuine, informed, and voluntary consent to the specific risk is shown.