The exact boundary between cameras that are "subminiature" and those that are merely "small" is the subject of debate among enthusiasts. Most broadly, cameras smaller than a typical small-format (135 or 828 rollfilm) camera are included.
In the interest of specificity, cameras that produce an image on the film smaller than the standard 135 format (24x36mm) are usually included in the genre. Some enthusiasts do not consider half-frame 135 (18x24mm) cameras "subminiature," while others still do not include the 110 cartridge format (12x17mm).
The Minox and Tessina subminiature cameras are most frequently associated with subminiature photography. Both are small, precision instruments that perhaps have more in common with a fine watch than a camera. Both are still in production today (2003), and film is still available.
A number of less expensive small cameras used the 16mm cartridge film format introduced by Minolta. Film is no longer made in this format but cartridges can be reloaded by hand.
The 110 format was also used by some subminiature cameras. Many of these were inexpensive but poorly manufactured, giving the format a bad name. However, a few quality cameras using 110 film were made by Minolta, Pentax, and Kodak. 110 film is still widely available.
Because of their small size and light weight, subminiature cameras can be readily carried in a pocket or purse and be available at all times.
The heyday of the subminiature camera ended with the introduction of the Canon AE-1 and Olympus OM-10, c. 1980. Both used 135 film, but were small, light, and easy to use.
Small digital cameras have all but replaced submini film cameras for covert surveillance.