atc - artist trading cards: "are miniature works of art created on 2 ½ X 3 ½ inch or 64 X 89 mm card stock.
they are originals, small editions and, most importantly, self-produced. anybody can produce them.
the idea is that you trade them with other people who produce cards, either at TRADING SESSIONS or wherever you meet another ATC trader in person.
it is important that you meet other people in person to trade - i.e. it is ok to trade by mail or to participate in editions but the main purpose of this performance is the trading session and the personal meeting.
It's not about money: participants in trading sessions and editions should not be charged any money: the point of the project is the exchange of cards as well as personal experience.
there are monthly TRADING SESSIONS at different places (zurich, calgary etc. see EVENTS) and you can start your own Trading Session wherever you live. there have been other TRADING SESSIONS at irregular intervals in other cities."
artist trading cards - Google Search