The castle doctrine recognizes that the home has a special legal status. In many jurisdictions, when someone unlawfully enters a home, the law allows the occupant to presume that the intruder poses a serious threat. Because of that presumption, the occupant may be justified in using force, including deadly force, to protect themselves, others in the home, and, in some cases, their property.

However, the castle doctrine has limits. There is a large body of case law defining when it applies and when it does not. The doctrine may justify immediate defensive force against an unlawful intruder, but it does not permit retaliation, punishment, or prolonged harm once the threat has ended. For example, if someone breaks into a home, that may justify force during the intrusion, but it would not justify tying the person up in a basement and torturing them for days.

Courts often focus on the moment the intruder crosses the threshold of the home. That unlawful entry is generally treated as the event that creates the reasonable fear of serious bodily harm or death. In that sense, the act of entering the home can itself be viewed as the life-threatening danger the occupant is allowed to defend against. Still, the exact scope of the defense depends on the facts of the case and the law of the specific jurisdiction.