A straitjacket is a garment shaped like a jacket with long sleeves that surpass the tips of the wearer's fingers. Its most typical use is restraining people who may cause harm to themselves or others. Once the wearer slides their arms into the sleeves, the person restraining the wearer crosses the sleeves against the chest and ties the ends of the sleeves to the back of the jacket, ensuring the arms are close to the chest with as little movement as possible.

Although straitjacket is the most common spelling, strait-jacket is also frequent. Straitjackets are also called camisoles.

The effect of a straitjacket as a restraint makes it of special interest in escapology. The straitjacket is also a staple prop in stage magic.

The straitjacket comes from the Georgian era of medicine. Physical restraint was used both as treatment for mental illness and to pacify patients in understaffed asylums.

Due to their strength, canvas and duck cloth are the most common materials for institutional straitjackets.