device used in weaving that is characterized by heddles—short lengths of wire or flat steel strips—used to deflect the warp to either side of the main sheet of fabric. The heddle is considered to be the most important single advance in the evolution of looms in general.

Originally heddles were movable rods, but later cords, wires, or steel bands were used. They are supported by the loom's harness, and each has an eyelet through which the warp threads pass.