Wedge, a device tapering to a thin edge or point, and used to split or pierce objects. A wedge is a simple machine, a device that reduces the force needed to do work. A wedge is often defined as two inclined planes placed back to back. However, there are two differences: (1) a wedge can have a curved surface, while that of an inclined plane must be flat; and (2) a wedge is moved, while an inclined plane remains in one place when work is being done.

The cutting edges of knives, axes, chisels, and other cutting instruments are wedges. Ice picks, nails, pins, needles, and other piercing devices also are wedges.

Less force is needed to drive a thin wedge than a thick one, but the thin wedge must be driven a greater distance to do as much work as the thick one. Theoretically, a wedge has a mechanical advantage equal to its length divided by its base. However, the friction involved in using wedges makes the theory meaningless.