A straitjacket is a garment shaped like a jacket with overlong sleeves. The ends of these can be tied to the back of the wearer, so their arms are kept close to their chest with possibility of only little movement.

They are used to restrain people who may otherwise cause harm to themselves and others, in hospitals for instance.

The straitjacket is also a staple prop in escapology, and sometimes used in sexual bondage (at between $150 and $300 for normal ones, and several times more for leather jackets, they're not widespread!).

Although straitjacket is the most common form, strait-jacket is also frequently used, and, in England, strait-waistcoat (Archaic). The spelling straight-jacket is a now valid alternative, although the original term came from strait meaning narrow or confined; thus straitjacket is preferable.

The security of a straitjacket depends very much on its size, which must be as small practicable to work effectively. You may notice on Posey jackets, the collars have a coloured band around them: this is to indicate the size; different colours for different sizes. Note also that the neck of a straitjacket is typically very wide: this is a safety-feature to stop the wearer from being able to choke on the front of the collar.

The arms of a jacket are typically sewn shut at the ends, so that you cannot poke your hands out of the ends of the sleeve; the arms are folded over the front of your body, and the straps (attached to, or part of, the sleeve-ends) are strapped together behind your back. It is necessary that this connection at the back be free to move, so that if you twist your arms, the strap-connection rotates away from your hands as you turn: if you were to fix these straps to the back of the jacket, it would be easier to undo.

Some jackets have a loop around the belly-area, through which you thread your arms before doing up the straps: this is just to stop you pulling arms over your head, which is an escapologist trick. Also, jackets should have a crotch-strap, to stop the wearer from pulling the entire jacket up over their head to remove it.

To remove a 'proper' straitjacket, it is almost always necessary to be able to dislocate one's shoulders: without this ability, only a gimmicked jacket, or a very oversized one can be escaped from. It is sometimes possible to get more room by pulling at the inside of the arms as they're being strapped, or by taking a deep breath and holding it whilst the jacket is done up: this is one of the reasons that you should have at least 2-3 people involved when fitting a straitjacket on someone who might use these tricks. It's possible for one person to put another willing volunteer into a straitjacket, but it takes two people to jacket a struggling person, and a third to keep an eye out for tricks such as holding the sleeves.

The straitjacket escape was popularized by Houdini. He first did it behind a curtain, forcing the audience to listen to thumps while watching a billowing curtain for many minutes. He found the trick went over better when the audience could see his struggles. Houdini could dislocate both his shoulders. His magician brother, Hardeen, who also did the escape, could only dislocate one shoulder.