A wagon or waggon is a heavy four-wheeled vehicle pulled by draught animals or on occasion by humans, used for transporting goods, commodities, agricultural materials, supplies and sometimes people.

Wagons are immediately distinguished from carts (which have two wheels) and from lighter four-wheeled vehicles primarily for carrying people, such as carriages. Animals such as horses, mules, or oxen usually pull wagons. One animal or several, often in pairs or teams may pull wagons. However, there are examples of human-propelled wagons, such as mining corfs.

A wagon was formerly called a wain and one who builds or repairs wagons is a wainwright. More specifically, a wain is a type of horse- or oxen-drawn, load-carrying vehicle, used for agricultural purposes rather than transporting people. A wagon or cart, usually four-wheeled; for example, a haywain, normally has four wheels, but the term has now acquired slightly poetical connotations, so is not always used with technical correctness. However, a two-wheeled "haywain" would be a hay cart, as opposed to a carriage. Wain is also an archaic term for a chariot. Wain can also be a verb, to carry or deliver, and has other meanings.

Contemporary or modern animal-drawn wagons may be of metal instead of wood and have regular wheels with rubber tires instead of traditional wagon wheels.

A person who drives wagons is called a "wagoner", a "teamster", a "bullocky" (Australia), a "muleteer", or simply a "driver".