Many states and the federal courts recognize defenses to criminal charges in limited circumstances when the defendant was under duress or committed the criminal offense out of necessity to avoid death or serious bodily injury. The definitions for these affirmative defenses vary from state to state and in the federal courts, with some jurisdictions treating them as the same defense, and others making the distinction that duress applies when a defendant committed the crime because someone forced them to do it, and necessity applies when the defendant was confronted with bad alternatives in an emergency situation and chose the best alternative.

The elements of the defense of duress or necessity are that (1) the defendant was facing an unlawful and imminent threat sufficient to create a reasonable apprehension of death or serious bodily injury; (2) the defendant had not recklessly or negligently placed himself in a situation where he would likely be forced to commit a criminal act; (3) the defendant had no reasonable, legal alternative to violating the law; and (4) the defendant could have reasonably believed that the commission of the criminal act would avoid the threatened harm.

Duress and necessity defenses to criminal charges may be located in a state’s court opinions or cases (common law) or in its statutes—usually in the penal or criminal code. Many states have pattern or form jury charges (questions and instructions) and include a question that may be given to the jury to determine whether the defendant’s conduct is excused by the defense of duress or necessity.

In Montana, the legal defenses of duress and necessity are recognized under certain circumstances when a person commits a crime to avoid death or serious bodily injury. These affirmative defenses are distinct in Montana law. Duress is applicable when an individual commits a crime because they were coerced by another person's threat of imminent harm. Necessity, on the other hand, is invoked when a person is faced with a dire situation and chooses the least harmful option among only bad alternatives. The key elements for these defenses in Montana include: facing an immediate and unlawful threat that could reasonably cause fear of death or serious bodily injury; not having placed oneself in the situation through recklessness or negligence; lacking a viable legal alternative to committing the crime; and reasonably believing that the criminal act was necessary to prevent the threatened harm. These defenses can be found in Montana's case law as well as its statutes, and they may be presented to a jury through pattern jury instructions that assess whether the defendant's actions can be excused by duress or necessity.