The Willys MB (pronounced / ˈ w ɪ l ɪ s /, Willis) and the Ford GPW, both formally called the U.S. Army truck, 1⁄4‑ton, 4×4, command reconnaissance, commonly known as the Willys Jeep, Jeep, or jeep, and sometimes referred to by its Standard Army vehicle supply number G-503, were highly successful American off-road capable, light military utility vehicles. Well over 600,000 were built to a single standardized design, for the United States and the Allied forces in World War II, from 1941 until 1945. This also made it (by its light weight) the world's first mass-produced four-wheel-drive car, built in six-figure numbers.

The 1⁄4-ton jeep became the primary light, wheeled, multi-role vehicle of the United States military and its allies. With some 640,000 units built, the 1⁄4‑ton jeeps constituted a quarter of the total military support motor vehicles that the U.S. produced during the war, and almost two-thirds of the 988,000 light 4WD vehicles produced, when counted together with the Dodge WC series. Large numbers of jeeps were provided to U.S. allies, including the Soviet Union at the time. Aside from large amounts of 11⁄2- and 21⁄2‑ton trucks, and 25,000 3⁄4‑ton Dodges, some 50,000 1⁄4‑ton jeeps were shipped to help Russia during WWII, against Nazi Germany's total production of just over 50,000 Kübelwagens, the jeep's primary counterpart.

Historian Charles K. Hyde wrote: In many respects, the jeep became the iconic vehicle of World War II, with an almost mythological reputation of toughness, durability, and versatility. It became the workhorse of the American military, replacing horses, other draft animals, and motorcycles in every role, from messaging and cavalry units to supply trains. In addition, improvised field modifications made the jeep capable of just about any other function soldiers could think of.