The MIM-104 Patriot is a mobile interceptor missile surface-to-air missile (SAM) system, the primary such system used by the United States Army and several allied states. It is manufactured by the U.S. defense contractor Raytheon and derives its name from the radar component of the weapon system. The AN/MPQ-53 at the heart of the system is known as the "Phased Array Tracking Radar to Intercept on Target", which is a backronym for "Patriot". In 1984, the Patriot system began to replace the Nike Hercules system as the U.S. Army's primary high to medium air defense (HIMAD) system and the MIM-23 Hawk system as the U.S. Army's medium tactical air defense system. In addition to defending against aircraft, Patriot is the U.S. Army's primary terminal-phase anti-ballistic missile (ABM) system. As of 2016^[update], the system is expected to stay fielded until at least 2040.

Patriot uses an advanced aerial interceptor missile and high-performance radar systems. Patriot was developed at Redstone Arsenal in Huntsville, Alabama, which had previously developed the Safeguard ABM system and its component Spartan and hypersonic Sprint missiles. The symbol for Patriot is a drawing of a Revolutionary War–era minuteman.

The MIM-104 Patriot has been widely exported. Patriot was one of the first tactical systems in the U.S. Department of Defense (DoD) to employ lethal autonomy in combat. The system saw poor performance in the 1991 Gulf War, without any confirmed interceptions of Iraqi Scud missiles, but made successful intercepts in the 2003 Iraq War. It has also been used by Saudi and Emirati forces in the Yemen conflict against Houthi missiles. In August 2014 batteries first downed UAVs when Israeli Air Defense Command engaged two Hamas drones during Operation Protective Edge. In September 2014, Patriot first shot down a crewed aircraft, when an Israeli battery intercepted a Syrian Air Force Sukhoi Su-24 . Since 2023, Patriot systems have been used by Ukraine in the Russo-Ukrainian war, downing Russian Su-34 and Su-35 fighters, Mi-8 helicopters, and Kinzhal ballistic missiles.

Prior to the Patriot, Raytheon was involved in a number of surface to air missile programs, including FABMDS (Field Army Ballistic Missile Defense System), AADS-70 (Army Air-Defense System – 1970) and SAM-D (Surface-to-Air Missile – Development). In 1975, the SAM-D missile successfully engaged a drone at the White Sands Missile Range. In 1976, it was renamed the PATRIOT Air Defense Missile System. The MIM-104 (Mobile Interceptor Missile 104) Patriot combined several new technologies, including the MPQ-53 passive electronically scanned array radar and track-via-missile guidance.

Full-scale development of the system began in 1976 and it was deployed in 1984. Patriot was used initially as an anti-aircraft system. In 1988, it received an upgrade providing limited capability against tactical ballistic missiles (TBM), designated PAC-1 (Patriot Advanced Capability 1). The most recent upgrade by manufacturer Lockheed Martin, designated PAC-3, is a nearly total system redesign of the interceptor missiles, this time designed from the outset with the capability to engage and destroy tactical ballistic missiles. The Army plans to upgrade the Patriot system as part of the Integrated Air and Missile Defense system designed to tie into a broader air defense architecture using an Integrated Battle Command System (IBCS).

The Patriot system has four major operational functions: communications, command and control, radar surveillance, and missile guidance. The four functions combine to provide a coordinated, secure, integrated, mobile air defense system.

The Patriot system is modular and highly mobile. A battery-sized element can be installed in less than an hour. All components, consisting of the fire control section (radar set, engagement control station, antenna mast group, electric power plant) and launchers, are truck- or trailer-mounted. The radar set and launchers (with missiles) are mounted on M860 semi-trailers, which are towed by Oshkosh M983 HEMTTs.

Missile reloading is accomplished using a M985 HEMTT truck with a Hiab crane on the back. This crane is larger than the standard Grove cranes found on regular M977 HEMTT and M985 HEMTT cargo body trucks. The crane truck, known as a Guided Missile Transporter (GMT), removes spent missile canisters from the launcher and replaces them with fresh missiles. Because the crane nearly doubles the height of the HEMTT when not stowed, crews informally refer to it as the "scorpion tail". A standard M977 HEMTT with a regular-sized crane is sometimes referred to as the Large Repair Parts Transporter (LRPT).^{[citation needed]}