Artist Trading Cards are individual art miniatures which pass hand to hand. Their current popularity among artists and hobbyists was sparked by M. Vänçi Stirnemann, who began trading sessions in Zurich, Switzerland, in 1997, and popularized ATCs via the internet.
[1]Artists have produced miniatures for trade or self-promotion in many eras and places, and the current trend is thus part of this larger context. Nevertheless, at the present time, the phrase Artist Trading Card is usually taken to refer to cards of the type promoted by Stirnemann. The only rule for these cards is their size (2.5 x 3.5 inches, the same as commercial trading cards, such as baseball cards and cards for trading card games). There are, however, certain conventions usually observed by those who make and trade these cards, such as the expectation that they be traded, not sold, and that they be created as unique works or small
limited editions of prints. Artists generally sign and date the back, and may also include a title and contact information. The face-to-face trading session is considered an integral part of the concept, although many people find each other via the internet and trade by mail.
See more at Wikipedia.org...