An anti-ship missile (AShM or ASM) is a guided missile that is designed for use against ships and large boats. Most anti-ship missiles are of the sea-skimming variety, and many use a combination of inertial guidance and active radar homing. A large number of other anti-ship missiles use infrared homing to follow the heat that is emitted by a ship; it is also possible for anti-ship missiles to be guided by radio command all the way.

Many anti-ship missiles can be launched from a variety of weapons systems including surface warships (also referred to as ship-to-ship missiles), submarines, bombers, fighter planes, patrol planes, helicopters, shore batteries, land vehicles, and, conceivably, even infantrymen firing shoulder-launched missiles. The term surface-to-surface missile (SSM) is used when appropriate. The longer-range anti-ship missiles are often called anti-ship cruise missiles. Several countries are also developing anti-ship ballistic missiles.

Both "AShM" and "ASM" are utilized interchangeably as an acronym for "anti-ship missile." "AShM" may be the preferred acronym when confusion with "air-to-surface missile" (commonly abbreviated as "ASM") may occur.

During the Cold War, the Soviet Union turned to a sea denial strategy concentrating on submarines, naval mines and the AShM. One of the first products of the decision was the SS-N-2 Styx missile. Further products were to follow, and they were soon loaded onto the Soviet Air Force's Tu-95 Bear and Tu-22 Blinder bombers, in the case of the air-launched KS-1 Komet.

In 1967, the Israeli Navy's destroyer Eilat was the first ship to be sunk by a ship-launched missile—a number of Styx missiles launched by Egyptian Komar-class missile boats off the Sinai Peninsula.

In the Indo-Pakistani War of 1971 the Indian Navy conducted two raids using Osa-class missile boats employing the Styx on the Pakistani naval base at Karachi. These raids resulted in the destruction or crippling of approximately two thirds of the Pakistani Navy. Major losses included two destroyers, a fleet oiler, an ammunition ship, approximately a dozen merchant ships, and numerous smaller craft. Major shore-based facilities, including fuel storage tanks and naval installations were also destroyed. The Osas returned to base without loss.

The Battle of Latakia in 1973 (during the Yom Kippur/Ramadan War) was the scene of the world's first combat between missile boats. In this battle, the Israeli Navy destroyed Syrian warships without suffering any damage, using electronic countermeasures and ruses for defense. After defeating the Syrian Navy the Israeli missile boats also sank a number of Egyptian warships, again without suffering any damage in return, thus achieving total naval supremacy for the rest of the war.

Anti-ship missiles were used in the 1982 Falklands War. The British warship HMS Sheffield, a Type 42 destroyer, was struck by a single air-launched Exocet and later sank as a result of the damage. The container ship Atlantic Conveyor was hit by two Exocets and burnt out and subsequently sank while under tow. HMS Glamorgan was damaged when she was struck by an MM38, a ship-launched version of the Exocet, fired from a launcher taken from the Argentine Navy destroyer ARA Comodoro Seguí and mounted on a trailer by Navy technicians, but she had taken evasive action that limited the damage.