Barbed Wire, also known as barbed wire (and frequently in dialect form spelled bob or bobbed), is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand(s). It is used to construct inexpensive fences and is used atop walls surrounding secured property. It is also a major feature of the fortifications in trench warfare (as a wire obstacle).

A person or animal trying to pass through or over barbed wire will suffer discomfort and possibly injury. Barbed wire fencing requires only fence posts, wire and fixing devices such as staples. It is simple to construct and quick to erect by an unskilled person.

Barbed wire was the first wire technology capable of restraining cattle. Wire fences were cheaper and easier to erect than their alternatives and when they became widely available in the late 19th century they made it affordable to fence much larger areas than before. They made intensive animal husbandry practical on a much larger scale.

Most barbed wire fences, while sufficient to discourage cattle, are passable by humans who can simply climb over the fence, or through the fence by stretching the gaps between the wires using non-barbed sections of the wire as hand holds. To prevent humans crossing, many prisons and other high-security installations construct fences with razor barbed wire, a variant which instead of occasional barbs features near-continuous cutting surfaces sufficient to injure unprotected persons who climb on it. A commonly seen alternative is the placement of a few strands of barbed wire at the top of a chain link fence. The limited mobility of someone climbing a fence makes passing conventional barbed wire more difficult. On some chain link fences these strands are attached to a bracket tilted 45 degrees towards the intruder, further increasing the difficulty.