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 California, both duress and necessity are recognized as affirmative defenses to criminal charges under certain circumstances. The defense of duress applies when a defendant commits a crime because they were forced to do so by the threat of immediate harm to themselves or others. Necessity, on the other hand, applies when a defendant is faced with a choice between two evils and must violate the law to prevent a greater harm. The elements required for these defenses typically include an imminent and unlawful threat of death or serious bodily injury, no prior recklessness or negligence by the defendant that led to the situation, no reasonable legal alternative to committing the crime, and a reasonable belief that the crime would prevent the threatened harm. These defenses are not just derived from common law but are also codified in California's penal code. California jury instructions may include questions related to duress or necessity to guide jurors in determining whether a defendant's actions are excusable under these defenses.