Black Light Theatre (in Czech černé divadlo) or simply Black Theatre, is a theatrical performance style characterized by the use of black box theatre augmented by black light illusion. This form of theatre originated from Asia and can be found in many places around the world. It has become a speciality of Prague, where many theatres use it.

The distinctive characteristics of "black theatre" are the use of black curtains, a darkened stage, and "black lighting" (UV light), paired with fluorescent costumes in order to create intricate visual illusions. This "black cabinet" technique was used by Georges Méliès, and by theatre revolutionary Stanislavsky. The technique, paired with the expressive artistry of dance, mime and acrobatics of the performers is able to create remarkable spectacles.

A key principal of Black Light Theatre is the inability of the human eye to distinguish black objects from a black background. This effect results in effective invisibility for any objects not illuminated by the 'black light'. The second optical principal behind Black Light Theatre is the effect of UV light on fluorescent objects. Black lights actually emit as much light as 'normal' lights, but at a frequency that humans cannot detect. While most objects either absorb UV light or reflect it back at the same frequency at which it came in, fluorescent objects absorb UV light then re-emit it a longer wavelength that human eyes can detect. The combined effect is that designers can make some objects appear as bright as if the room were fully lighted, while making other objects appear as dark as if the room were completely dark.

A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation (UV) in the long-wave (near ultraviolet, UVA) range, and little visible light. Other types of ultraviolet lamp emit large amounts of visible light along with the ultraviolet; however, a "black light" usually refers to a lamp that has a dark blue optical filtering material in the glass envelope of the bulb (or the lamp housing) which blocks most of the visible light, so the lamp emits mostly ultraviolet. Ultraviolet radiation is invisible, but a small fraction of visible light passes through the filtering material, with wavelengths no longer than 400-410 nm, and as a result, when operating the lamp emits a dim purple or violet glow. Wood's glass is one type of filtering material which is used in black lights.

Black light sources may be made from specially designed fluorescent lamps, mercury vapor lamps, light-emitting diodes, or incandescent lamps. In most black lights the blue optical filter material to block visible light is in the glass envelope of the light bulb, but in some types there is a separate filter glass in the lamp housing. In medicine, forensics, and some other scientific fields, such a light source is referred to as a Wood's lamp (named after Robert Williams Wood).