A hostage is a person seized by an abductor in order to compel another party, one which places a high value on the liberty, well-being and safety of the person seized—such as a relative, employer, law enforcement, or government—to act, or refrain from acting, in a certain way, often under threat of serious physical harm or death to the hostage(s) after expiration of an ultimatum. The Encyclopædia Britannica Eleventh Edition defines a hostage as "a person who is handed over by one of two belligerent parties to the other or seized as security for the carrying out of an agreement, or as a preventive measure against certain acts of war."

A party who seizes one or more hostages is known as a hostage-taker; if the hostages are present voluntarily, then the receiver is known as a host.

In civil society, along with kidnapping for ransom and human trafficking (often willing to ransom its captives when lucrative or to trade on influence), hostage taking is a criminal activity. In the military context, hostages are distinct from prisoners of war—despite prisoners being used as collateral in prisoner exchange—and hostage taking is regarded as a war crime.

On occasion, hostage taking is an impulsive act of desperation, as when a criminal act goes awry, the criminal has lethal force available, and a bystander becomes hasty collateral, despite the prospects for evading justice remaining poor, now soon surrounded by lethal force with intent as well as criminal prosecution for a serious additional crime, should the hostage taker survive the escalated stand-off (not always the intent; see suicide by cop). These confrontations are extremely dramatic, and are prominent in the public eye, despite being rather uncommon. Hostage taking is sometimes the only way to enact a plan, hence tactical, such as certain forms of prison escape, especially as treated in film.

At the other extreme, it can be an entirely calculated business venture by what amounts to organized crime. Before venturing into regimes known for lax rule of law, it is commonplace for affluent travellers and business persons to obtain kidnap and ransom insurance, though this will be less effective if the kidnapper's game plan transmutes into political extortion.

Parental child abduction is not generally considered hostage taking because there is usually no threat of harm to the child and no ultimatum concerning the return of the child (though there are cases where the leverage obtained within the failed parental relationship is more desired than the child), but otherwise hostage taking and kidnapping are prone to blend together. When the goal is strictly financial, the primary lens is one of extortion, even in the face of a severe threat to the safety of the captive person if the financial negotiation fails; conversely, when the goal is political or geopolitical, the primary lens is terrorism.