A head harness is a device used in BDSM activities. It is made of interconnected straps designed to encircle the human head; the straps are generally secured by buckles that fasten at the back of the head. Head harnesses are most commonly used to provide points of attachments to secure various kinds of gags, such as ball gags, although they also have other uses, such as providing attachment points for other forms of bondage, or may be used simply for their psychological effect. Head harnesses may also function as a gag by themselves, by restricting the ability to open the mouth, or have a mouth cover as an integral part. They may also include a blindfold, possibly detachable.
Where a gag is used, or the harness functions as a gag, the entire assembly is often called a harness gag; as with all forms of gagging, the general risks of gags apply.
Head harnesses, like many other forms of bondage, also have the effect of creating a sense of objectification and erotic helplessness in the wearer, which can be erotic for the wearer, or for those observing them. Many head harnesses are designed with straps that pass in front of the wearer's eyes, restricting their vision, and further increasing the sense of objectification and erotic subjection. Some have full blindfolds.