Barbed wire, also known as barb wire is a type of steel fencing wire constructed with sharp edges or points arranged at intervals along the strands. 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, even by an unskilled person. Barbed wire was the first wire technology capable of restraining cattle. Wire fences are cheaper and easier to erect than their alternatives (one such alternative is Osage orange, a thorny bush that is time-consuming to transplant and grow).