In contract law, force majeure (/ˌfɔːrs məˈʒɜːr/ FORSS mə-ZHUR; French: [fɔʁs maʒœʁ]) is a common clause in contracts which essentially frees both parties from liability or obligation when an extraordinary event or circumstance beyond the control of the parties, such as a war, strike, riot, crime, epidemic, or sudden legal change prevents one or both parties from fulfilling their obligations under the contract. Force majeure often includes events described as acts of God, though such events remain legally distinct from the clause itself. In practice, most force majeure clauses do not entirely excuse a party's non-performance but suspend it for the duration of the force majeure.

Force majeure is generally intended to include occurrences beyond the reasonable control of a party, and therefore would not cover:

Under international law, it refers to an irresistible force or unforeseen event beyond the control of a state, making it materially impossible to fulfill an international obligation. Accordingly, it is related to the concept of a state of emergency.

Force majeure in any given situation is controlled by the law governing the contract, rather than general concepts of force majeure. Contracts often specify what constitutes force majeure via a clause in the agreement. So, the liability is decided per contract and neither by statute nor by principles of general law. The first step to assess whether—and how—force majeure applies to any particular contract is to ascertain the law of the country (state) which governs the contract.

Time-critical and other sensitive contracts may be drafted to limit the shield of this clause where a party does not take reasonable steps (or specific precautions) to prevent or limit the effects of the outside interference, either when they become likely or when they actually occur. A force majeure may work to excuse all or part of the obligations of one or both parties. For example, a strike might prevent timely delivery of goods, but not timely payment for the portion delivered.

A force majeure may also be the overpowering force itself, which prevents the fulfillment of a contract. In that instance, it is actually the impossibility or impracticability defenses.

In the military, "force majeure" has a slightly different meaning. It refers to an event, either external or internal, that happens to a vessel or aircraft that allows it to enter normally restricted areas without penalty. An example would be the Hainan Island incident, where a U.S. Navy aircraft landed at a Chinese military airbase after a collision with a Chinese fighter in April 2001. Under the principle of force majeure, the aircraft was allowed to land without interference. Similarly, the 2023 Chinese balloon incident, in which a Chinese surveillance balloon was discovered in U.S. air space, the Chinese government stated that this "was entirely an accident caused by force majeure".

The importance of the force majeure clause in a contract, particularly one of any length in time, cannot be overstated as it relieves a party from an obligation under the contract (or suspends that obligation). What is permitted to be a force majeure event or circumstance can be the source of much controversy in the negotiation of a contract and a party should generally resist any attempt by the other party to include something that should, fundamentally, be at the risk of that other party. For example, in a coal-supply agreement, the mining company may seek to have "geological risk" included as a force majeure event; however, the mining company should be doing extensive exploration and analysis of its geological reserves and should not even be negotiating a coal-supply agreement if it cannot take the risk that there may be a geological limit to its coal supply from time to time. The outcome of that negotiation, of course, depends on the relative bargaining power of the parties and there will be cases where force majeure clauses can be used by a party effectively to escape liability for bad performance.