The M113 is a fully tracked armored personnel carrier that has formed the backbone of the United States Army's mechanized infantry units from the time of its first fielding in Vietnam in April 1962. The M113 was the most widely used armored vehicle of the U.S. Army in the Vietnam War, earning the nickname 'Green Dragon' by some people, but largely known as an APC and ACAV (armored cavalry assault vehicle) by the allied forces, as it was used to break through heavy thickets in the midst of the jungle to attack and overrun enemy positions.

The M113 introduced new aluminum armor that made the vehicle much lighter than earlier vehicles; it was thick enough to protect the crew and passengers against small arms fire but light enough that the vehicle was air transportable and moderately amphibious. In the U.S. Army, the M113 series have long been replaced as front-line combat vehicles by the M2 and M3 Bradley, but large numbers are still used in support roles such as armored ambulance, mortar carrier, engineer vehicle, command vehicle, etc. The Army's Heavy Brigade Combat Teams are currently equipped with around 6,000 M113s and 4,000 Bradleys.

An armoured personnel carrier (APC) is an armoured fighting vehicle designed to transport infantry to the battlefield. APCs are sometimes known to troops as 'battle taxis' or 'battle buses'.

APCs are usually armed with only a machine gun although variants carry recoilless rifles, anti-tank guided missiles (ATGMs), or mortars. They are not usually designed to take part in a direct-fire battle, but to carry troops to the battlefield safe from shrapnel and ambush. They may have wheels or tracks.

Examples include the American M113 (tracked), the British FV 432 (tracked), the French VAB (wheeled), the Dutch/German GTK Boxer (wheeled) and the Soviet BTR (wheeled). Infantry fighting vehicles, by contrast, are more heavily armed and armoured and are designed for direct combat.

During World War I, when the tank was developed, the British Mark V* tank was designed with a small passenger compartment to carry troops. By some definitions this can be considered the first armoured personnel carrier. The first specialised APC was the Mark IX of 1918.